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. 2002 Jan;76(2):783–790. doi: 10.1128/JVI.76.2.783-790.2002

The Genome of Swinepox Virus

C L Afonso 1,*, E R Tulman 1, Z Lu 1, L Zsak 1, F A Osorio 2, C Balinsky 1, G F Kutish 1, D L Rock 1
PMCID: PMC136851  PMID: 11752168

Abstract

Swinepox virus (SWPV), the sole member of the Suipoxvirus genus of the Poxviridae, is the etiologic agent of a worldwide disease specific for swine. Here we report the genomic sequence of SWPV. The 146-kbp SWPV genome consists of a central coding region bounded by identical 3.7-kbp inverted terminal repeats and contains 150 putative genes. Comparison of SWPV with chordopoxviruses reveals 146 conserved genes encoding proteins involved in basic replicative functions, viral virulence, host range, and immune evasion. Notably, these include genes with similarity to genes for gamma interferon (IFN-γ) receptor, IFN resistance protein, interleukin-18 binding protein, IFN-α/β binding protein, extracellular enveloped virus host range protein, dUTPase, hydroxysteroid dehydrogenase, superoxide dismutase, serpin, herpesvirus major histocompatibility complex inhibitor, ectromelia virus macrophage host range protein, myxoma virus M011L, variola virus B22R, four ankyrin repeat proteins, three kelch-like proteins, five vaccinia virus (VV) A52R-like family proteins, and two G protein-coupled receptors. The most conserved genomic region is centrally located and corresponds to the VV region located between genes F9L and A38L. Within the terminal 13 kbp, colinearity is disrupted and multiple poxvirus gene homologues are absent or share a lower percentage of amino acid identity. Most of these differences involve genes and gene families with likely functions involving viral virulence and host range. Three open reading frames (SPV018, SPV019. and SPV020) are unique for SWPV. Phylogenetic analysis, genome organization, and amino acid identity indicate that SWPV is most closely related to the capripoxvirus lumpy skin disease virus, followed by the yatapoxvirus yaba-like disease virus and the leporipoxviruses. The gene complement of SWPV better defines Suipoxvirus within the Chordopoxvirinae subfamily and provides a basis for future genetic comparisons.

Swinepox virus (SWPV) is the sole member of the Suipoxvirus genus, one of eight genera within the Chordopoxvirinae subfamily of the Poxviridae. It is responsible for swinepox, a disease that occurs worldwide and is associated with poor sanitation (18).

Swinepox is most severe in young pigs (up to 4 months of age), where morbidity may approach 100% (18, 30). Adults generally develop a mild, self-limiting form of the disease, with lesions in hairless skin areas that remain localized at the sites of entry (7, 18, 30). In adults, macroscopic cutaneous lesions pass through the characteristic stages of poxviral lesions with a very short vesicular phase that usually does not exhibit fluid exudates (9, 18, 30). SWPV infection in swine is characterized by slight fever and inflammation of local lymph nodes. Generalized infection and viremia are not observed (22). The source and the reservoir of SWPV are infected swine (18). Lice are considered the primary agents of transmission, but occasional horizontal transmission may occur through contact of nasal and oral secretions with skin abrasions (18).

SWPV infects only swine. Of several mammalian and avian species tested, only rabbits produced a nonproductive infection after intradermal inoculation (8). The host range specificity of SWPV and its ability to induce solid protective immunity have stimulated interest in using SWPV as a host range-restricted vaccine vector (14, 41, 45).

Current molecular data describing the SWPV genome consist of restriction endonuclease analysis and limited DNA sequence analysis of the terminal regions (4, 12, 25, 26, 34). Given the interest in developing more effective SWPV vaccines and expression vectors, we have sequenced and analyzed the genome of a pathogenic SWPV. These data provide a comprehensive view of the SWPV genome and further elucidate the relationship of SWPV to other chordopoxviruses (ChPVs). Furthermore, they define the gene complement that underlies the virulence and restricted host range of SWPV.

MATERIALS AND METHODS

SWPV DNA isolation, cloning, sequencing, and sequence analysis.

SWPV genomic DNA was extracted from pig kidney cells infected with virus obtained from a pig litter congenitally infected during an outbreak of swinepox in Nebraska in 1999. These animals displayed foci of full-thickness epithelial necrosis distributed over the entire skin and tongue. Random DNA fragments were obtained by incomplete enzymatic digestion with Tsp509I endonuclease (New England Biolabs, Beverly, Mass.), and DNA fragments of 1.0 to 6.0 kbp were cloned and sequenced as previously described (2). Reaction products were run on a PRISM 3700 automated DNA sequencer (PE Biosystems, Foster City, Calif.). Sequence data were assembled with the Phrap software program and gaps were closed as described previously (1, 11), with confirmatory assemblies performed using CAP3 (19). The final DNA consensus sequence represented on average eightfold redundancy at each base position.

Genome DNA composition, structure, repeats, and restriction enzyme patterns were analyzed as previously described (1) using the Genetics Computer Group version 10 software package (10). Open reading frames (ORFs) longer than 30 codons were evaluated for coding potential as previously described (2). All potentially coding ORFs and ORFs greater than 60 codons were evaluated by homology searches as previously described (1, 2). Using these criteria, 150 ORFs were annotated as potential genes. Gene family regions were analyzed with Geanfammer (32) and promoters were analyzed with Genetics Computer Group MEME programs (10), and annotation was as previously described (1, 2). The vaccinia virus (VV) A52R-like protein family was clustered from a nonredundant peptide database of all known poxvirus sequences using the CLUS program (23) and BLASTP2 scores of greater than 115. Phylogenetic comparisons were done with the PHYLO_WIN software package (15).

Nucleotide sequence accession number.

The SWPV genome sequence was assigned GenBank accession no. AF410153.

RESULTS AND DISCUSSION

Organization of the SWPV genome.

SWPV genome sequences were assembled into a contiguous sequence of 146,454 bp, which agrees with a previous restriction enzyme-based size estimate of 148 to 150 kbp and previously published restriction enzyme maps (26). Because the hairpin loops were not sequenced, the leftmost nucleotide was arbitrarily designated base 1. The nucleotide composition is 72.5% A+T and is uniformly distributed. As found in other poxviruses, the SWPV genome contains a 139,023-bp central coding region bounded by two identical inverted terminal repeat (ITR) regions of 3.7 kbp (Fig. 1). The most-terminal nucleotides of the assembled sequence contain a 34-bp perfect tandem repeat which is part of a 65-bp imperfect repeat. Based on these data and published restriction digests, we estimated that heterogeneity of termini containing repeats may account for an additional 200 to 1,200 bp (26).

FIG. 1.

FIG. 1.

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Linear map of the SWPV genome. ORFs are numbered from left to right based on the position of the methionine initiation codon. ORFs transcribed to the right are located above the horizontal line; ORFs transcribed to the left are below. Genes with similar functions and members of gene families are colored as indicated. ITRs are represented as black bars below the ORF map.

SWPV has a compact gene arrangement with almost no overlapping ORFs and no evidence of introns or large regions of noncoding DNA. SWPV contains 150 putative genes which encode proteins of 53 to 1,959 amino acids, of which 146 are poxvirus homologues (Fig. 1; Table 1). The conserved central core (SPV021 to SPV125), which is colinear with VV F9L to A38L, contains 106 genes, most of which are involved in basic replicative functions. In terminal genomic regions, genes are oriented toward the ends, while in the central region, genes are oriented in both directions, often grouped in clusters with identical orientation. SWPV promoters resemble other ChPV promoters (Table 1). As is found in other poxviruses, many of the 30 putative early genes are members of gene families and putative host range genes, while the 45 genes containing the VV late promoter sequence (TAAATG) at the ATG codon (28) encode many of the conserved virion-associated poxviral proteins (Table 1).

TABLE 1.

SWPV ORFs

ORF Position (length, codons) SPV accession no.a Best match
Predicted structure and/or functiond Promoter typee LSDV
YLDV
MYX
VV
Species Accession no.a BLASTP2 score % Id.j Length (aa)c ORFf % Id.j ORFg % Id.j ORFh % Id.j ORFi % Id.j
SPV001 736-287 (150) LSDV AF325528 498 62 145 A52R family protein LSDV001 62 6L 41 M003.1 45 B15R 41
SPV002 1323-814 (170) ShPVb P18388 195 39 113 TM LSDV002 39 M003.2 29
SPV003 2452-1433 (340) P32231 YLDV AJ293568 539 38 335 MHC class 1 α chain-like protein, TM E 2L 38
SPV004 2772-2497 (92) P32230 LSDV AF325528 217 46 91 LSDV004 46 150R 42 M004.1 44
SPV005 3630-2824 (269) Q08520 Human U45983 497 37 267 GPCR, TM LSDV011 38 7L/145R 36
SPV006 5285-3696 (530) P32228 RFV AF170722 824 33 523 Kelch-like protein LSDV151 27 140R 28 M008L 34 A55R 29
SPV007 6038-5331 (236) P32227 YLDV AJ293568 444 43 217 A52R family protein LSDV009 29 3L 43 K7R 35
SPV008 6885-6064 (274) P32226 LSDV AF325528 435 37 257 IFN-γ receptor, SP, TM E LSDV008 37 M007 25 B8R 28
SPV009 7385-6921 (155) P32225 LSDV AF325528 309 35 150 LAP/PHD-finger protein, TM LSDV010 35 5L 34 M153R 36
SPV010 7705-7448 (86) P32224 LSDV AF325528 248 49 85 elF2α-like PKR inhibitor E LSDV014 49 12L 48 M156R 40 K3L 44
SPV011 8146-7745 (134) P32223 LSDV AF325528 308 44 129 IL-18 binding protein LSDV015 44 14L 42
SPV012 8672-8172 (167) P32222 LSDV AF325528 168 34 171 Integral membrane protein, apoptosis regulator E LSDV017 34 16L 31 M011L 27
SPV013 9153-8728 (142) P32208 LSDV AF325528 505 68 141 dUTPase LSDV018 68 17L 65 M012L 59 F2L 58
SPV014 9576-9205 (124) P32221 YLDV AJ293568 243 38 124 E 18L 38 M013L 36
SPV015 11205-9604 (534) P32206 LSDV AF325528 1,100 40 564 Kelch-like protein LSDV019 40 19L 38 M014L 39 F3L 28
SPV016 12243-11284 (320) P32209 VAR U18338 1,341 77 320 Ribonucleotide reductase (small subunit) TM E LSDV020 78 20L 78 M015L 74 F4L 76
SPV017 12529-12272 (86) P32220 LSDV AF325528 179 38 86 SP, TM LSDV021 38 21L 33 M016L 28
SPV018 12789-12571 (73) P32219
SPV019 13012-12803 (70) P32218 E
SPV020 13142-12942 (67) P32217 SP, TM
SPV021 14156-13512 (215) P32207 LSDV AF325528 754 64 216 TM L LSDV024 64 24L 50 M019L 52 F9L 45
SPV022 15462-14143 (440) P32216 LSDV AF325528 1,996 80 435 Ser/Thr protein kinase, virus assembly L LSDV025 80 25L 76 M020L 77 F10L 72
SPV023 16562-15486 (359) VV AF095689 448 31 351 E LSDV026 34 F11L 31
SPV024 18530-16596 (645) LSDV AF325528 1,546 51 631 EEV maturation, TM E LSDV027 51 A26L 49 M021L 46 F12L 39
SPV025 19678-18566 (371) AJ249689 ShPV AF199594 1,499 76 368 EEV envelope protein, virus assembly LSDV028 75 27L 74 M022L 73 F13L 56
SPV026 19915-19727 (63) AL109739 72 30 53
SPV027 20589-20146 (148) LSDV AF325528 514 66 148 LSDV029 66 29L 62 M024L 49 F15L 60
SPV028 21311-20661 (217) LSDV AF325528 502 44 218 LSDV030 44 30L 39 M025L 36 F16L 42
SPV029 21372-21680 (103) YLDV AJ293568 388 72 100 DNA binding virion core phosphoprotein L LSDV031 71 31R 72 M026L 70 F17R 62
SPV030 23092-21683 (470) LSDV AF325528 1,877 75 474 Poly(A) polymerase PAP LSDV032 75 32L 71 M027L 74 E1L 65
SPV031 25324-23129 (732) LSDV AF325528 2,089 55 714 LSDV033 55 33L 50 M028L 53 E2L 44
SPV032 25909-25379 (177) YLDV AJ293568 471 50 180 PKR inhibitor, host range E LSDV034 49 34L 50 M029L 50 E3L 34
SPV033 26552-25938 (205) LSDV AF325528 795 71 199 RNA polymerase subunit RPO30 E LSDV036 71 35L 70 M030R 68 E4L 68
SPV034 26660-28363 (568) LSDV AF325528 2,267 73 568 E/L LSDV037 73 37R 68 M032R 67 E6R 60
SPV035 28370-29155 (262) LSDV AF325528 1,147 80 265 ER-localized protein, TM LSDV038 80 38R 74 M033R 81 E8R 66
SPV036 32190-29167 (1008) MYX AF170726 4,123 75 1,008 DNA polymerase E LSDV039 75 39L 68 M034L 75 E9L 66
SPV037 32223-32510 (96) MYX AF170726 382 67 96 Potential redox protein, virus assembly LSDV040 69 40R 71 M035R 67 E10R 66
SPV038 34587-32557 (677) MYX AF170726 1,521 42 678 E LSDV042 43 42L 43 M036L 42 O1L 34
SPV039 35664-34726 (313) LSDV AF325528 1,187 72 314 DNA binding virion core protein, virus assembly L LSDV043 72 43L 67 M038L 70 I1L 66
SPV040 35892-35668 (75) RFV AF170722 202 53 73 TM L LSDV044 52 44L 53 M039L 57 12L 59
SPV041 36756-35896 (287) LSDV AF325528 915 65 276 DNA binding phosphoprotein LSDV045 65 45L 61 M040L 60 I3L 53
SPV042 39041-36771 (757) VAR P32984 2,727 66 751 Ribonucleotide reductase (large chain) I4L 66
SPV043 39324-39091 (78) LSDV AF325528 264 56 78 IMV membrane protein, SP, TM L LSDV046 56 46L 55 M041L 51 I5L 31
SPV044 40497-39343 (385) LSDV AF325528 1,181 57 394 TM LSDV047 57 47L 50 M042L 52 I6L 51
SPV045 41791-40493 (433) LSDV AF325528 1,792 75 433 Virion core protein L LSDV048 75 48L 74 M043L 74 I7L 68
SPV046 41797-43839 (681) LSDV AF325528 2,315 64 681 NPH-II, RNA helicase LSDV049 64 49R 61 M044R 62 I8R 58
SPV047 45620-43842 (593) LSDV AF325528 2,158 67 595 Metalloprotease, virion morphogenesis L LSDV050 67 50L 63 M045L 64 G1L 57
SPV048 45946-46641 (232) LSDV AF325528 768 63 222 Putative transcriptional elongation factor LSDV051 63 52R 48 M047R 55 G2R 44
SPV049 45952-45620 (111) RFV AF170722 384 63 111 TM L LSDV052 58 51L 54 M046L 63 G3L 47
SPV050 46958-46584 (125) LSDV AF325528 488 70 124 Glutaredoxin 2, virion morphogenesis, L LSDV053 70 53L 64 M048L 64 G4L 43
SPV051 46963-48279 (439) LSDV AF325528 1,486 63 438 LSDV054 63 54R 54 M049R 52 G5R 46
SPV052 48285-48473 (63) LSDV AF325528 286 87 63 RNA polymerase subunit RPO7 E LSDV055 87 55R 84 M050R 82 G5.5R 77
SPV053 48476-48994 (173) LSDV AF325528 539 60 169 TM LSDV056 60 56R 55 M051R 59 G6R 43
SPV054 50144-49002 (381) LSDV AF325528 1,227 65 378 Virion core protein, TM L LSDV057 65 57L 60 M052L 54 G7L 53
SPV055 50174-50953 (260) LSDV AF325528 1,245 91 260 Late transcription factor VLTF-1, TM LSDV058 91 58R 88 M053R 85 G8R 83
SPV056 50949-52016 (356) LSDV AF325528 1,038 58 336 Myristylated protein LSDV059 58 59R 56 M054R 52 G9R 45
SPV057 52020-52766 (249) LSDV AF325528 1,111 85 245 Myristylated IMV envelope protein, TM L LSDV060 85 60R 81 M055R 75 L1R 67
SPV058 52799-53080 (94) LSDV AF325528 242 50 85 TM E LSDV061 50 61R 40 M056R 29 L2R 31
SPV059 54025-53066 (320) LSDV AF325528 1,205 70 320 L LSDV062 70 62L 65 M057R 65 L3L 49
SPV060 54051-54809 (253) LSDV AF325528 1,078 81 253 DNA-binding virion core protein VP8 L LSDV063 81 63R 77 M058R 79 L4R 62
SPV061 54824-55210 (129) LSDV AF325528 412 64 126 TM L LSDV064 64 64R 54 M059R 52 L5R 50
SPV062 55167-55610 (148) P23332 ShPV P19746 451 60 148 L LSDV065 60 65R 57 M060R 53 J1R 53
SPV063 55625-56167 (181) M64000 ShPV P16600 640 68 175 Thymidine kinase, SP LSDV066 68 66R 66 M061R 67 J2R 64
SPV064 56225-56779 (185) P23333 ShPV P19747 467 48 187 Host range protein E LSDV067 48 67R 45 M062R 41 C7L 39
SPV065 56835-57833 (333) RFV AF170722 1,430 79 333 Poly(A) polymerase PAPs LSDV068 77 68R 72 M065R 78 J3R 72
SPV066 57751-58305 (185) LSDV AF325528 816 81 185 RNA polymerase subunit RPO22 LSDV069 81 69R 75 M066R 72 J4R 66
SPV067 58715-58314 (134) RFV AF170722 541 68 132 LSDV070 67 70L 65 M067L 67 J5L 60
SPV068 58782-62636 (1285) LSDV AF325528 5,865 84 1,285 RNA polymerase subunit RPO147 LSDV071 84 71R 84 M068R 84 J6R 80
SPV069 63169-62651 (173) ShPV AF124517 718 78 171 Protein tyrosine phosphatase, virus assembly L LSDV072 78 72L 72 M069L 73 H1L 61
SPV070 63184-63753 (190) ShPV AF124517 789 73 190 TM LSDV073 73 73R 67 M070R 71 H2R 65
SPV071 64742-63771 (324) LSDV AF325528 1,075 61 320 IMV envelope protein p35, TM L LSDV074 61 74L 54 M071L 54 H3L 40
SPV072 67148-64746 (801) LSDV AF325528 3,378 78 801 RNA polymerase-associated protein RAP94 L LSDV075 78 75L 76 M072L 75 H4L 69
SPV073 67315-67857 (181) YLDV AJ293568 436 50 181 Late transcription factor VLTF-4 E LSDV076 46 76R 50 M073R 48 H5R 37
SPV074 67896-68855 (320) LSDV AF325528 1,204 72 315 DNA topoisomerase LSDV077 72 77R 61 M074R 66 H6R 61
SPV075 68867-69313 (149) LSDV AF325528 499 68 145 L LSDV078 68 78R 53 M075R 55 H7R 43
SPV076 69320-71839 (840) LSDV AF325528 3,320 72 842 mRNA capping enzyme (large subunit) LSDV079 72 79R 70 M076R 71 D1R 65
SPV077 72244-71807 (146) YLDV AJ293568 355 47 149 Virion protein LSDV080 46 80L 47 M077L 46 D2L 40
SPV078 72249-72980 (244) LSDV AF325528 469 39 241 Virion protein LSDV081 39 81R 37 M078R 37 D3R 34
SPV079 72980-73630 (217) RFV AF170126 926 72 216 Uracil DNA glycosylase, DNA replication LSDV082 73 82R 73 M079R 72 D4R 69
SPV080 73663-76020 (786) LSDV AF325528 3,324 76 786 NTPase, DNA replication, TM L LSDV083 76 83R 77 M080R 76 D5R 68
SPV081 76020-77924 (635) LSDV AF325528 3,004 90 635 Early transcription factor VETFs, TM L LSDV084 90 84R 87 M081R 87 D6R 81
SPV082 77952-78434 (161) LSDV AF325528 731 81 160 RNA polymerase subunit RPO18 L LSDV085 81 85R 75 M082R 77 D7R 63
SPV083 78507-79145 (213) LSDV AF325528 744 69 213 mutT motif E LSDV086 69 86R 64 M084R 61 D9R 57
SPV084 79145-79870 (242) RFV P32097 709 56 237 mutT motif, gene expression regulator L LSDV087 55 87R 61 M085R 59 D10R 45
SPV085 81766-79871 (632) LSDV AF325528 2,606 77 632 NPH-I, transcription termination factor L LSDV088 77 88L 73 M086L 74 D11L 69
SPV086 82647-81787 (287) Q08512 LSDV AF325528 1,259 80 287 mRNA capping enzyme (small subunit), VITF E/L LSDV089 80 89L 82 M087L 76 D12L 77
SPV087 84330-82678 (551) Q08517 YLDV AJ293568 2,347 78 550 Rifampin resistance protein, IMV assembly LSDV090 77 90L 78 M088L 76 D13L 70
SPV088 84807-84358 (150) LSDV AF325528 529 65 150 Late transcription factor VLTF-2 L LSDV091 65 91L 62 M089L 64 A1L 57
SPV089 85531-84860 (224) LSDV AF325528 1,039 87 225 Late transcription factor VLTF-3 LSDV092 87 92L 84 M090L 85 A2L 80
SPV090 85755-85531 (75) LSDV AF325528 297 72 75 L LSDV093 72 93L 56 M091L 66 8.9 kDa* 50
SPV091 87720-85765 (652) LSDV AF325528 2,736 78 656 Virion core protein P4b L LSDV094 78 94L 78 M092L 75 A3L 67
SPV092 88230-87769 (154) LSDV AF325528 407 52 158 Virion core protein, virion morphogenesis L LSDV095 52 95L 38 M093L 32 A4L 27
SPV093 88271-88756 (162) LSDV AF325528 542 65 170 RNA polymerase subunit RPO19 L LSDV096 65 96R 57 M094R 65 A5R 59
SPV094 89877-88759 (373) MYX AF170726 1,529 77 372 LSDV097 78 97L 70 M095L 77 A6L 56
SPV095 92035-89903 (711) LSDV AF325528 3,027 80 714 Early transcription factor VETFL LSDV098 80 98L 77 M096L 80 A7L 71
SPV096 92097-92972 (292) LSDV AF325528 1,090 74 288 Intermediate transcription factor VITF-3 LSDV099 74 99R 68 M097R 70 A8R 62
SPV097 93226-92975 (84) LSDV AF325528 352 84 78 IMV membrane protein, morphogenesis, SP, TM L LSDV100 84 100L 83 M098L 80 A9L 69
SPV098 95941-93230 (904) LSDV AF325528 3,491 72 904 Virion core protein P4a L LSDV101 72 101L 68 M099L 65 A10L 51
SPV099 95956-96888 (311) YMTV AB015885 1,237 76 314 L LSDV102 75 102R 77 M100R 75 A11R 53
SPV100 97433-96900 (178) MYX AF170726 435 66 153 Virion core protein L LSDV103 57 103L 62 M101L 66 A12L 52
SPV101 97657-97454 (68) LSDV AF325528 190 57 68 IMV membrane protein, TM L LSDV104 57 104L 54 M102L 48 A13L 33
SPV102 98006-97725 (94) YLDV AJ293568 420 87 94 IMV membrane protein, SP, TM L LSDV105 82 105L 87 M103L 70 A14L 55
SPV103 98184-98026 (53) YLDV AJ293568 235 84 52 Virulence factor, SP LSDV106 75 106L 84 M104L 76 A14.5 56
SPV104 98458-98177 (94) YMTV AB015885 263 51 94 L LSDV107 49 107L 46 M105L 50 A15L 47
SPV105 99581-98445 (379) LSDV AF325528 1,387 66 379 Putative myristylated membrane protein, TM L LSDV108 66 108L 60 M106L 60 A16L 52
SPV106 100192-99611 (194) YLDV AJ293568 692 69 194 Phosphorylated IMV membrane protein, TM L LSDV109 64 109L 69 M107L 54 A17L 42
SPV107 100207-101643 (479) LSDV AF325528 1,623 65 480 DNA helicase, transcriptional elongation, TM LSDV110 65 110R 63 M108R 61 A18R 57
SPV108 101845-101630 (72) LSDV AF325528 292 76 72 L LSDV111 76 111L 72 M109L 76 A19L 63
SPV109 102189-103472 (428) LSDV AF325528 1,266 57 427 DNA polymerase proces- sivity factor E LSDV112 57 113R 48 M111R 54 A20R 46
SPV110 102190-101849 (114) MYX AF170726 391 64 114 TM LSDV113 62 112L 62 M110L 64 A21L 59
SPV111 103453-103950 (166) VAR X76268 653 71 164 DNA processing E LSDV114 64 114R 71 M112R 61 A22R 71
SPV112 103979-105124 (382) LSDV AF325528 1,274 66 383 Intermediate transcription factor VITF-3 LSDV115 66 115R 63 M113R 62 A23R 59
SPV113 105129-108614 (1162) LSDV AF325528 5,459 89 1,156 RNA polymerase subunit RPO132 LSDV116 89 116R 87 M114R 86 A24R 82
SPV114 109061-108615 (149) LSDV AF325528 345 48 144 Fusion protein, virus assembly L LSDV117 48 117L 41 M115L 52 A27L 45
SPV115 109485-109054 (144) ShPV P16718 539 71 139 SP, TM L LSDV118 71 118L 64 M116L 65 A28L 50
SPV116 110404-109499 (302) MYX AF170726 1,137 65 302 RNA polymerase subunit RPO35 E LSDV119 68 119L 63 M117L 65 A29L 59
SPV117 110597-110376 (74) YLDV AJ293568 220 63 73 Virion protein, maturation LSDV120 61 120L 63 M118L 57 A30L 51
SPV118 111542-110787 (252) LSDV AF325528 1,109 82 252 DNA packaging, virus assembly LSDV121 82 121L 79 M120L 80 A32L 58
SPV119 111706-112260 (185) LSDV AF325528 356 44 179 EEV glycoprotein, TM LSDV122 44 122R 41 M121R 38 A33R 30
SPV120 112290-112796 (169) YLDV AJ293568 644 64 169 EEV protein LSDV123 58 123R 64 M122R 60 A34R 50
SPV121 112809-113363 (185) LSDV AF325528 444 45 177 E LSDV124 45 124R 46 M123R 39 A35R 36
SPV122 113341-114282 (314) LSDV AF325528 785 53 288 TM LSDV125 53 125R 39 M124R 44
SPV123 114313-114909 (199) YLDV AJ293568 244 40 191 EEV glycoprotein, TM LSDV126 36 126R 40 M125R 28 A36R 25
SPV124 114913-115752 (280) LSDV AF325528 752 51 271 TM L LSDV127 51 127R 40 M126R 44 A37R 28
SPV125 116661-115783 (293) MYX AF170726 576 38 281 CD47-like protein, SP, TM LSDV128 31 128L 30 M128L 38 A38L 21
SPV126 116801-117178 (126) LSDV AF325528 128 33 112 LSDV129 33 M130R 28
SPV127 117250-117486 (79a) LSDV AF325528 180 54 75 LSDV130 54 132R 40
SPV128 118520-117489 (344) YLDV AJ293568 959 53 343 Hydroxysteroid dehydrogenase-like protein E 133L 53 A44L 45
SPV129 118565-119053 (163) LSDV AF325528 550 64 159 Superoxide dismutase-like protein LSDV131 64 M131R 59 A45R 31
SPV130 119089-120765 (559) LSDV AF325528 1,912 63 558 DNA ligase LSDV133 63 M133R 61 A50R 50
SPV131 120870-126746 (1959) LSDV AF325528 5,419 56 2,007 VAR B22R homologue, TM LSDV134 56 135R 50 M134R 50
SPV132 126727-127758 (344) YLDV AJ293568 408 31 346 IFN-α/β binding protein, SP LSDV135 32 136R 31 M135R 29 B18R 28
SPV133 127790-128326 (179) LSDV AF325528 358 46 156 A52R family protein LSDV136 46 137R 30 M136R 42 K7R 25
SPV134 128372-129355 (328) LSDV AF325528 882 50 335 E LSDV137 50 138R 39 M137R 39 A51R 33
SPV135 129411-129974 (188) MYX AF170726 539 58 187 A52R family protein LSDV136 35 139R 45 M139R 58 A52R 38
SPV136 129994-131715 (574) YLDV AJ293568 1,317 44 564 Kelch-like protein, TM LSDV151 29 140R 44 M140R 43 A55R 31
SPV137 131727-132653 (309) LSDV AF325528 1,069 65 297 Ser/Thr protein kinase, DNA replication LSDV139 65 142R 55 M142R 61 B1R 46
SPV138 132666-133403 (246) RFV L26342 597 49 226 N1R/p28-like host range RING finger protein LSDV140 46 143R 41 M143R 49
SPV139 133451-134146 (232) MYX AF170726 497 45 215 EEV host range protein, TM LSDV141 42 144R 44 M144R 45 C3L 34
SPV140 134184-135080 (299) LSDV AF325528 887 58 296 Tyrosine protein kinase-like protein LSDV143 58 M147R 48
SPV141 135128-137032 (635) LSDV AF325528 1,515 46 627 Ankyrin repeat protein LSDV145 46 146R 29 M148R 38 B4R 26
SPV142 137100-138554 (485) RFV AF170722 1,183 46 484 Ankyrin repeat protein, TM LSDV147 43 146R 38 M149R 44 B4R 24
SPV143 138662-139951 (430) LSDV AF325528 778 39 426 Ankyrin repeat protein E LSDV148 39 147R 33 M148R 29 B4R 22
SPV144 140003-141481 (493) LSDV AF325528 776 34 492 Ankyrin repeat protein E LSDV152 34 148R 28 M005 30 B4R 28
SPV145 141494-142453 (320) L21931 LSDV AF325528 600 41 334 Serpin E LSDV149 41 149R 38 M151R 33 C12L 31
SPV146 142522-143631 (370) Q08520 Human AY016370 589 37 343 GPCR, TM LSDV011 37 145R/7L 38 M139R 29
SPV147 143683-143958 (92) P32230 LSDV AF325528 217 46 91 LSDV153 46 150R 42 M004.1 44
SPV148 144003-145022 (340) P32231 YLDV AJ293568 539 38 335 MHC class I α chain-like protein, SP, TM E 2L 38
SPV149 145132-145641 (170) ShPV P18388 195 39 113 TM LSDV155 39 M003.2 29
SPV150 145719-146168 (150) LSDV AF325528 498 62 145 A52R family protein LSDV156 65 6L 41 M003.1 45 B15R 41
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a

Accession numbers are from the GenBank or SwissProtein database.

b

ShPV, sheeppox virus.

c

aa, amino acids.

d

Function was deduced either from the degree of similarity to known genes or from the presence of Prosite signatures. TM, a Z score of >1.96 was used for the prediction of transmembrane (TM) domains with the MEMSAT computer program (21). SP, N-terminal signal peptide (Z score of >3.5 within 40 amino acids of the N terminus determined using the SIGCLEAVE computer program [ftp://ftp.ebi.ac.uk/pub/software/unix/EMBOSS/] [43]).

e

Putative promoters (E, early; I, intermediate; L, late) were identified as previously described (2).

f

Best-matching ORF from the LSDV genome (accession no. AF325528).

g

Best-matching ORF from the YLDV genome (accession no. AJ293568).

h

Best-matching ORF from the MYX genome (accession no. AF170726).

i

Best-matching ORF from the VV Copenhagen genome (accession no. M35027), with the exception of the 8.9-kDa protein (*) (accession no. P07608), which corresponds to the VV Ankara strain.

j

Percentage of amino acid identity in the BLASTP2 analysis.

Gene families and duplicated genes with probable host range functions include those for extracellular enveloped virus proteins (EEV) (SPV119 and SPV120), ankyrins (SPV141, SPV142, SPV143, and SPV144), kelch-like proteins (SPV006, SPV015, and SPV136), A52-like proteins (SPV001, SPV007, SPV133, SPV135, and SPV150), G protein-coupled receptors (SPV005 and SPV146), major histocompatibility complex (MHC) class I α chain-like proteins (SPV003 and SPV148), and proteins of unknown function (SPV002, SPV004, SPV147, and SPV149).

Nucleic acid biogenesis, virion structure, and virion assembly.

SWPV contains most of the conserved poxviral genes involved in basic replicative functions, including 26 genes encoding RNA polymerase subunits; mRNA transcription initiation, elongation, and termination factors; and enzymes which direct posttranscriptional processing of viral mRNA (28) (Table 1). Also present in SWPV are seven ChPV homologues necessary for, or potentially involved in, DNA replication (SPV036, SPV074, SPV079, SPV080, SPV109, SPV130, and SPV137) (28).

SWPV nucleotide metabolism genes are similar to those found in the capripoxviruses and leporipoxviruses, except for the addition in SWPV of the large subunit of ribonucleotide reductase (6, 42, 44). These SWPV proteins potentially include homologues of thymidine kinase, dUTP pyrophosphatase, and a large and a small subunit of ribonucleotide reductase (Table 1). Interestingly, the large subunit of ribonucleotide reductase is absent from lumpy skin disease virus (LSDV), myxoma virus (MYX), and rabbit fibroma virus (RFV), all of which are closely related viruses (Table 1 and Fig. 2).

FIG. 2.

FIG. 2.

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Comparison of SPV068 to ChPV RNA polymerase subunit RPO147. Proteins were aligned with ClustalW. Complete amino acid sequences were used to generate the unrooted tree with Melanoplus sanguinipes entomopoxvirus RPO147 as the outgroup. The neighbor-joining algorithm with Poisson correction for multiple substitution and 1,000 bootstraps was used as implemented by the Phylip package (15). The figure represents the ChPV subtree. Bootstrap values greater than 80% are in boldface. The bar indicates changes per 100 amino acids. Similar results were obtaining using maximum-likelihood and maximum-parsimony analysis (data not shown).

SWPV encodes 35 homologues of conserved poxviral structural proteins and those involved in virion morphogenesis and assembly (Table 1). These include proteins present in the virion core; proteins present in the intracellular mature virus (IMV) and associated membranes; potential enzymes involved in protein modification, DNA packaging, and redox activity; and at least four VV proteins found in or associated with the release of EEV (Table 1). SWPV, like LSDV, molluscum contagiosum virus, and fowlpox virus, lacks an obvious homologue of the VV IMV membrane protein D8L, a cell surface binding protein which is present in leporipoxviruses.

Host-related functions.

SWPV contains genes which likely function in modulation or evasion of host immune responses, modulation or inhibition of host cell apoptosis, or aspects of cell or tissue tropism. Many potential SWPV host range genes are homologues to genes present in other poxviruses. However, SWPV does contain a unique complement of these genes which likely dictate specific host range properties.

Some SWPV proteins are potentially secreted and are likely involved in the disruption or modulation of host immune responses as indicated by their similarity to other secreted immunomodulators and by the presence of potential signal peptide sequences. These include homologues of the gamma interferon (IFN-γ) receptor (SPV008), IFN-α/β binding protein (SPV132), and interleukin-18 (IL-18) binding protein (SPV011) (Table 1).

SWPV also contains predicted membrane-localized immunomodulatory proteins, including two homologues of G-protein coupled CC chemokine receptors (GPCR), and a CD47 homologue (6, 24, 25, 33) (Table 1). SPV005 is a truncated form of a GPCR lacking the first extracellular domain, while SPV146 resembles the complete receptor. SPV003 and SPV148 resemble cellular MHC class I α chain-like proteins, the molluscum contagiosum virus MC80R and yaba-like disease virus (YLDV) 2L gene products. These SWPV gene products have α1, -2, and -3 domains, one RGD motif, and three of the four cysteine residues required for formation of disulfide bonds. They differ from the MC80R gene product in that they lack the 50-amino-acid amino-terminal extension. SWPV MHC gene products also lack similarity to the transmembrane and cytoplasmic domains of cellular MHC homologues. In human and mouse cytomegaloviruses, another viral MHC homologue has been shown to interfere with NK cell-mediated clearance; however, the MC80R gene product appears to differ from herpesvirus homologues in the kinetics of complex formation and intracellular protein localization (36). The apparent lack of similarities in protein domains suggests that SWPV MHC-like genes may have other functions. SPV009 is similar to the leukemia-associated protein domain (LAP) and plant homeobox domain (PHD) finger protein found in LSDV, YLDV, and leporipoxviruses. Similar proteins in gammaherpesviruses are known to down-regulate expression of cellular MHC and NK cell activation ligands (20, 31, 40)

Several SWPV proteins may have intracellular immune modulation or immune evasion functions. These include homologues of VV double-stranded RNA-dependent protein kinase inhibitors (SPV010 and SPV032) which confer resistance to the antiviral effects of IFN (Table 1). Poxviral serine proteinase inhibitors (serpins) are known to perform anti-inflammatory roles, and the single serpin encoded in SWPV (SPV145) is similar to LSDV 149, YLDV 149R, and MYX M151R (25). Notably, SPV001, SPV007, SPV133, SPV135, and SPV150 are similar to members of the poxviral gene family which includes VV A52R (family 5 [38]) (data not shown). Although the functions of most of these genes are not known, VV A52R has been shown to function as an antagonist for host cell IL-1 receptor (IL-1R) and Toll-like receptor-mediated intracellular signaling and IL-18R-mediated induction of NF-κβ activation (5). The potential for IL-1 or Toll-like receptor inhibition by a family of SWPV proteins is significant considering the role of IL-1 or Toll-like receptor signaling in induction of innate immune and inflammatory responses (13).

SWPV encodes homologues of several other poxviral proteins known to affect virus virulence, virus growth in specific cell types, and/or cellular apoptotic responses (Table 1). These include homologues of VV C7L host range (SPV064) and A14.5L virulence (SPV103) proteins, the MYX M011L apoptosis regulator protein (SPV012), a serpin homologue (SPV145), and RFV N1R (ectromelia virus p28 host range factor) (SPV138). SWPV also encodes four proteins containing ankyrin motifs (SPV141 to SPV144) (Table 1). Poxviral ankyrin genes have been associated with host range functions in MYX, cowpox virus, and VV and may inhibit virally induced apoptosis (16, 29, 39). It has been suggested that specific complements of ankyrin genes dictate poxvirus host range, and the same is probably true for SWPV (3, 37).

SWPV has homologues of poxvirus genes resembling those for cellular enzymes (Table 1). SPV128, SPV129, and SPV140 resemble hydroxysteroid dehydrogenase, copper-zinc superoxide dismutase, and tyrosine protein kinase, respectively.

SWPV encodes several homologues of poxvirus proteins of unknown function, including the VV 8.9-kDa protein (SPV090), which interacts with VV morphogenesis proteins, and the variola virus (VAR) B22R putative membrane protein (SPV131) (Table 1) (27). SPV006, SPV015, and SPV136 are similar the Drosophila kelch protein and other poxvirus kelch-like proteins (Table 1). SPV018, SPV019, and SPV020 lack homology to other known genes.

Comparison of SWPV to other ChPVs.

SWPV is very similar to other ChPVs in overall genome structure and composition, as indicated by the presence of a central conserved core of 106 genes surrounded by regions containing many genes with apparent host range functions and the ITRs. The SWPV genome is highly colinear with the genomes of other ChPVs (Table 1) (2, 17, 35, 44). In comparison with VV, eight genes are absent in the SWPV central core. These include homologues of E11L (virion component), D8L (similar to carbonic anhydrase), A25L and A26L (A-type inclusion proteins), O2L (glutaredoxin), A31R, E5R, and E7R. A homologue of VV gene C7L (SPV064), which is believed to encode a host range factor, has been inserted between SPV063 and SPV065 (J2R and J3R homologues). Colinearity decreases toward the genome ends and disappears at the ITR. The SWPV left and right noncolinear regions contain only 44 genes and lack most VV gene homologues found in HindIII restriction fragments B, C, K, N, M, and F.

Gene colinearity is most conserved compared to LSDV, YLDV, and the leporipoxviruses (Table 1). SWPV overall amino acid identity is highest to proteins of LSDV (60% average), followed by those of YLDV (57%) and the leporipoxviruses (57%). Phylogenetic analysis of all of the SWPV genes located in the conserved central region indicates a close relationship among suipoxviruses (SWPV), capripoxviruses (LSDV), leporipoxviruses (MYX and RFV), and yatapoxviruses (Yaba monkey tumor virus [YMTV]) and a clear separation of these from other vertebrate poxvirus genera (orthopoxviruses, avipoxviruses, and molluscipoxviruses) (Fig. 2 and data not shown). These four genera also share genomic features which are different from those of orthopoxviruses, molluscipoxviruses, and avipoxviruses. Most notable is the absence of VV homologues A25L, A26L, and A31R and the insertion of one to three copies of the VV C7L homologue between J2R and J3R.

The terminal genomic regions of SWPV encode many proteins with probable functions involving host range, virulence, and immune modulation. At the amino acid level, many of these SWPV proteins are less similar to other poxvirus homologues than are viral proteins encoded in the conserved central core region. Two SWPV proteins located in terminal regions (SPV005 and SPV146) are most similar to cellular proteins (Table 1). Although closely related, SWPV contains eight genes that are absent in LSDV, including those for MHC class I proteins (two copies), ribonucleotide reductase (large subunit), hydroxysteroid dehydrogenase, and an M013L homologue and the unique SWPV genes SPV018, SPV019, and SPV020. In contrast, 13 genes present in LSDV are absent in SWPV, including those for epidermal-like growth factor, IL-10, IL-1R, VV C4/C10 like protein, endoplasmic reticulum (ER)-localized apoptosis regulator, immunoglobulin domain Ox-2 like homologue, VV E5R, E11L, K4L, F8L, and N1L and the novel LSDV genes LSDV026 and LSDV161. The absence of these genes from SWPV may explain the relatively reduced virulence and narrow host range of this virus.

Conclusions.

The genome sequence of SWPV has been determined. The high degree of similarity in genomic organization, gene content, and amino acid composition to viruses from the Suipoxvirus, Capripoxvirus, Yatapoxvirus, and Leporipoxvirus genera indicates a close structural and functional relationship among these genera. Although the highest conservation occurs in genes involved in basic replicative functions, including mRNA biogenesis, DNA replication, and virion structure and assembly, significant similarities exist among genes performing other functions. A unique complement of SWPV genes in the terminal genomic regions likely function in virulence, host range, and immune evasion. The relative paucity of SWPV genes with known host range function in other poxviruses may be responsible for the low pathogenicity of this virus in swine and for its narrow host range. An improved understanding of SWPV-host interactions will permit the engineering of novel vaccine viruses and expression vectors with enhanced efficacy and greater versatility.

Acknowledgments

We thank A. Zsak and A. Ciupryk for excellent technical assistance.

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