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. 1995 Dec;177(24):7078–7085. doi: 10.1128/jb.177.24.7078-7085.1995

Identification of two targets of the type III protein secretion system encoded by the inv and spa loci of Salmonella typhimurium that have homology to the Shigella IpaD and IpaA proteins.

K Kaniga 1, D Trollinger 1, J E Galán 1
PMCID: PMC177584  PMID: 8522512

Abstract

An important virulence factor of Salmonella spp. is their ability to gain access to host cells. A type III secretion system encoded in the inv and spa loci of these organisms is essential for this phenotype. We have identified two proteins, SipA and SipD, whose secretion from the bacterial cells is dependent on this system. The genes encoding these proteins are located at centisome 63 on the S. typhimurium chromosome, immediately downstream of the previously identified sipB and sipC genes (K. Kaniga, S. Tucker, D. Trollinger, and J. E. Galán, J. Bacteriol. 177:3965-3971, 1995). Nucleotide sequence analysis of the genes encoding these proteins indicated that SipA and SipD have significant sequence similarity to the Shigella IpaA and IpaD proteins. A nonpolar null mutation in sipD rendered S. typhimurium severely deficient for entry into cultured epithelial cells. In addition, this mutant strain exhibited increased secretion of a selected group of proteins whose export is controlled by the inv- and spa-encoded translocon. In contrast, a nonpolar mutation in sipA did not result in an invasion defect or in a significant decreased in virulence in a mouse model of infection. In addition, we have found an open reading frame immediately downstream of SipA that encodes a predicted protein with significant similarity to a family of acyl carrier proteins.

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Selected References

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  1. Allaoui A., Sansonetti P. J., Parsot C. MxiD, an outer membrane protein necessary for the secretion of the Shigella flexneri lpa invasins. Mol Microbiol. 1993 Jan;7(1):59–68. doi: 10.1111/j.1365-2958.1993.tb01097.x. [DOI] [PubMed] [Google Scholar]
  2. Allaoui A., Sansonetti P. J., Parsot C. MxiJ, a lipoprotein involved in secretion of Shigella Ipa invasins, is homologous to YscJ, a secretion factor of the Yersinia Yop proteins. J Bacteriol. 1992 Dec;174(23):7661–7669. doi: 10.1128/jb.174.23.7661-7669.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Allaoui A., Woestyn S., Sluiters C., Cornelis G. R. YscU, a Yersinia enterocolitica inner membrane protein involved in Yop secretion. J Bacteriol. 1994 Aug;176(15):4534–4542. doi: 10.1128/jb.176.15.4534-4542.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Altmeyer R. M., McNern J. K., Bossio J. C., Rosenshine I., Finlay B. B., Galán J. E. Cloning and molecular characterization of a gene involved in Salmonella adherence and invasion of cultured epithelial cells. Mol Microbiol. 1993 Jan;7(1):89–98. doi: 10.1111/j.1365-2958.1993.tb01100.x. [DOI] [PubMed] [Google Scholar]
  5. Altschul S. F., Gish W., Miller W., Myers E. W., Lipman D. J. Basic local alignment search tool. J Mol Biol. 1990 Oct 5;215(3):403–410. doi: 10.1016/S0022-2836(05)80360-2. [DOI] [PubMed] [Google Scholar]
  6. Andrews G. P., Hromockyj A. E., Coker C., Maurelli A. T. Two novel virulence loci, mxiA and mxiB, in Shigella flexneri 2a facilitate excretion of invasion plasmid antigens. Infect Immun. 1991 Jun;59(6):1997–2005. doi: 10.1128/iai.59.6.1997-2005.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Andrews G. P., Maurelli A. T. mxiA of Shigella flexneri 2a, which facilitates export of invasion plasmid antigens, encodes a homolog of the low-calcium-response protein, LcrD, of Yersinia pestis. Infect Immun. 1992 Aug;60(8):3287–3295. doi: 10.1128/iai.60.8.3287-3295.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Arlat M., Van Gijsegem F., Huet J. C., Pernollet J. C., Boucher C. A. PopA1, a protein which induces a hypersensitivity-like response on specific Petunia genotypes, is secreted via the Hrp pathway of Pseudomonas solanacearum. EMBO J. 1994 Feb 1;13(3):543–553. doi: 10.1002/j.1460-2075.1994.tb06292.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Behlau I., Miller S. I. A PhoP-repressed gene promotes Salmonella typhimurium invasion of epithelial cells. J Bacteriol. 1993 Jul;175(14):4475–4484. doi: 10.1128/jb.175.14.4475-4484.1993. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Bergman T., Erickson K., Galyov E., Persson C., Wolf-Watz H. The lcrB (yscN/U) gene cluster of Yersinia pseudotuberculosis is involved in Yop secretion and shows high homology to the spa gene clusters of Shigella flexneri and Salmonella typhimurium. J Bacteriol. 1994 May;176(9):2619–2626. doi: 10.1128/jb.176.9.2619-2626.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Chang Y. F., Young R., Struck D. K. Cloning and characterization of a hemolysin gene from Actinobacillus (Haemophilus) pleuropneumoniae. DNA. 1989 Nov;8(9):635–647. doi: 10.1089/dna.1.1989.8.635. [DOI] [PubMed] [Google Scholar]
  12. Chéret G., Mattheakis L. C., Sor F. DNA sequence analysis of the YCN2 region of chromosome XI in Saccharomyces cerevisiae. Yeast. 1993 Jun;9(6):661–667. doi: 10.1002/yea.320090612. [DOI] [PubMed] [Google Scholar]
  13. Collazo C. M., Zierler M. K., Galán J. E. Functional analysis of the Salmonella typhimurium invasion genes invl and invJ and identification of a target of the protein secretion apparatus encoded in the inv locus. Mol Microbiol. 1995 Jan;15(1):25–38. doi: 10.1111/j.1365-2958.1995.tb02218.x. [DOI] [PubMed] [Google Scholar]
  14. Cooper C. L., Boyce S. G., Lueking D. R. Purification and characterization of Rhodobacter sphaeroides acyl carrier protein. Biochemistry. 1987 May 19;26(10):2740–2746. doi: 10.1021/bi00384a013. [DOI] [PubMed] [Google Scholar]
  15. Debellé F., Sharma S. B. Nucleotide sequence of Rhizobium meliloti RCR2011 genes involved in host specificity of nodulation. Nucleic Acids Res. 1986 Sep 25;14(18):7453–7472. doi: 10.1093/nar/14.18.7453. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Devereux J., Haeberli P., Smithies O. A comprehensive set of sequence analysis programs for the VAX. Nucleic Acids Res. 1984 Jan 11;12(1 Pt 1):387–395. doi: 10.1093/nar/12.1part1.387. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Donnenberg M. S., Yu J., Kaper J. B. A second chromosomal gene necessary for intimate attachment of enteropathogenic Escherichia coli to epithelial cells. J Bacteriol. 1993 Aug;175(15):4670–4680. doi: 10.1128/jb.175.15.4670-4680.1993. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Eichelberg K., Ginocchio C. C., Galán J. E. Molecular and functional characterization of the Salmonella typhimurium invasion genes invB and invC: homology of InvC to the F0F1 ATPase family of proteins. J Bacteriol. 1994 Aug;176(15):4501–4510. doi: 10.1128/jb.176.15.4501-4510.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Fenselau S., Balbo I., Bonas U. Determinants of pathogenicity in Xanthomonas campestris pv. vesicatoria are related to proteins involved in secretion in bacterial pathogens of animals. Mol Plant Microbe Interact. 1992 Sep-Oct;5(5):390–396. doi: 10.1094/mpmi-5-390. [DOI] [PubMed] [Google Scholar]
  20. Galán J. E., Curtiss R., 3rd Cloning and molecular characterization of genes whose products allow Salmonella typhimurium to penetrate tissue culture cells. Proc Natl Acad Sci U S A. 1989 Aug;86(16):6383–6387. doi: 10.1073/pnas.86.16.6383. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Galán J. E., Ginocchio C., Costeas P. Molecular and functional characterization of the Salmonella invasion gene invA: homology of InvA to members of a new protein family. J Bacteriol. 1992 Jul;174(13):4338–4349. doi: 10.1128/jb.174.13.4338-4349.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Galán J. E., Ginocchio C. The molecular genetic bases of Salmonella entry into mammalian cells. Biochem Soc Trans. 1994 May;22(2):301–306. doi: 10.1042/bst0220301. [DOI] [PubMed] [Google Scholar]
  23. Genin S., Boucher C. A. A superfamily of proteins involved in different secretion pathways in gram-negative bacteria: modular structure and specificity of the N-terminal domain. Mol Gen Genet. 1994 Apr;243(1):112–118. doi: 10.1007/BF00283883. [DOI] [PubMed] [Google Scholar]
  24. Ginocchio C. C., Olmsted S. B., Wells C. L., Galán J. E. Contact with epithelial cells induces the formation of surface appendages on Salmonella typhimurium. Cell. 1994 Feb 25;76(4):717–724. doi: 10.1016/0092-8674(94)90510-x. [DOI] [PubMed] [Google Scholar]
  25. Ginocchio C., Pace J., Galán J. E. Identification and molecular characterization of a Salmonella typhimurium gene involved in triggering the internalization of salmonellae into cultured epithelial cells. Proc Natl Acad Sci U S A. 1992 Jul 1;89(13):5976–5980. doi: 10.1073/pnas.89.13.5976. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Gough C. L., Genin S., Lopes V., Boucher C. A. Homology between the HrpO protein of Pseudomonas solanacearum and bacterial proteins implicated in a signal peptide-independent secretion mechanism. Mol Gen Genet. 1993 Jun;239(3):378–392. doi: 10.1007/BF00276936. [DOI] [PubMed] [Google Scholar]
  27. Gough C. L., Genin S., Zischek C., Boucher C. A. hrp genes of Pseudomonas solanacearum are homologous to pathogenicity determinants of animal pathogenic bacteria and are conserved among plant pathogenic bacteria. Mol Plant Microbe Interact. 1992 Sep-Oct;5(5):384–389. doi: 10.1094/mpmi-5-384. [DOI] [PubMed] [Google Scholar]
  28. Groisman E. A., Ochman H. Cognate gene clusters govern invasion of host epithelial cells by Salmonella typhimurium and Shigella flexneri. EMBO J. 1993 Oct;12(10):3779–3787. doi: 10.1002/j.1460-2075.1993.tb06056.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Hackett M., Guo L., Shabanowitz J., Hunt D. F., Hewlett E. L. Internal lysine palmitoylation in adenylate cyclase toxin from Bordetella pertussis. Science. 1994 Oct 21;266(5184):433–435. doi: 10.1126/science.7939682. [DOI] [PubMed] [Google Scholar]
  30. Hansen L., von Wettstein-Knowles P. The barley genes Acl1 and Acl3 encoding acyl carrier proteins I and III are located on different chromosomes. Mol Gen Genet. 1991 Oct;229(3):467–478. doi: 10.1007/BF00267471. [DOI] [PubMed] [Google Scholar]
  31. He S. Y., Huang H. C., Collmer A. Pseudomonas syringae pv. syringae harpinPss: a protein that is secreted via the Hrp pathway and elicits the hypersensitive response in plants. Cell. 1993 Jul 2;73(7):1255–1266. doi: 10.1016/0092-8674(93)90354-s. [DOI] [PubMed] [Google Scholar]
  32. Hoiseth S. K., Stocker B. A. Aromatic-dependent Salmonella typhimurium are non-virulent and effective as live vaccines. Nature. 1981 May 21;291(5812):238–239. doi: 10.1038/291238a0. [DOI] [PubMed] [Google Scholar]
  33. Huang H. C., Xiao Y., Lin R. H., Lu Y., Hutcheson S. W., Collmer A. Characterization of the Pseudomonas syringae pv. syringae 61 hrpJ and hrpI genes: homology of HrpI to a superfamily of proteins associated with protein translocation. Mol Plant Microbe Interact. 1993 Jul-Aug;6(4):515–520. doi: 10.1094/mpmi-6-515. [DOI] [PubMed] [Google Scholar]
  34. Issartel J. P., Koronakis V., Hughes C. Activation of Escherichia coli prohaemolysin to the mature toxin by acyl carrier protein-dependent fatty acylation. Nature. 1991 Jun 27;351(6329):759–761. doi: 10.1038/351759a0. [DOI] [PubMed] [Google Scholar]
  35. Jones B. D., Falkow S. Identification and characterization of a Salmonella typhimurium oxygen-regulated gene required for bacterial internalization. Infect Immun. 1994 Sep;62(9):3745–3752. doi: 10.1128/iai.62.9.3745-3752.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Kaniga K., Bossio J. C., Galán J. E. The Salmonella typhimurium invasion genes invF and invG encode homologues of the AraC and PulD family of proteins. Mol Microbiol. 1994 Aug;13(4):555–568. doi: 10.1111/j.1365-2958.1994.tb00450.x. [DOI] [PubMed] [Google Scholar]
  37. Kaniga K., Tucker S., Trollinger D., Galán J. E. Homologs of the Shigella IpaB and IpaC invasins are required for Salmonella typhimurium entry into cultured epithelial cells. J Bacteriol. 1995 Jul;177(14):3965–3971. doi: 10.1128/jb.177.14.3965-3971.1995. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Klein P., Delisi C. Prediction of protein structural class from the amino acid sequence. Biopolymers. 1986 Sep;25(9):1659–1672. doi: 10.1002/bip.360250909. [DOI] [PubMed] [Google Scholar]
  39. Klein P., Kanehisa M., DeLisi C. The detection and classification of membrane-spanning proteins. Biochim Biophys Acta. 1985 May 28;815(3):468–476. doi: 10.1016/0005-2736(85)90375-x. [DOI] [PubMed] [Google Scholar]
  40. Lee C. A., Jones B. D., Falkow S. Identification of a Salmonella typhimurium invasion locus by selection for hyperinvasive mutants. Proc Natl Acad Sci U S A. 1992 Mar 1;89(5):1847–1851. doi: 10.1073/pnas.89.5.1847. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Lidell M. C., Hutcheson S. W. Characterization of the hrpJ and hrpU operons of Pseudomonas syringae pv. syringae Pss61: similarity with components of enteric bacteria involved in flagellar biogenesis and demonstration of their role in HarpinPss secretion. Mol Plant Microbe Interact. 1994 Jul-Aug;7(4):488–497. doi: 10.1094/mpmi-7-0488. [DOI] [PubMed] [Google Scholar]
  42. Lo R. Y., Strathdee C. A., Shewen P. E. Nucleotide sequence of the leukotoxin genes of Pasteurella haemolytica A1. Infect Immun. 1987 Sep;55(9):1987–1996. doi: 10.1128/iai.55.9.1987-1996.1987. [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Macnab R. M. Genetics and biogenesis of bacterial flagella. Annu Rev Genet. 1992;26:131–158. doi: 10.1146/annurev.ge.26.120192.001023. [DOI] [PubMed] [Google Scholar]
  44. Magnuson K., Jackowski S., Rock C. O., Cronan J. E., Jr Regulation of fatty acid biosynthesis in Escherichia coli. Microbiol Rev. 1993 Sep;57(3):522–542. doi: 10.1128/mr.57.3.522-542.1993. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Maurelli A. T. Virulence protein export systems in Salmonella and Shigella: a new family or lost relatives? Trends Cell Biol. 1994 Jul;4(7):240–242. doi: 10.1016/0962-8924(94)90116-3. [DOI] [PubMed] [Google Scholar]
  46. Michiels T., Cornelis G. R. Secretion of hybrid proteins by the Yersinia Yop export system. J Bacteriol. 1991 Mar;173(5):1677–1685. doi: 10.1128/jb.173.5.1677-1685.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Michiels T., Vanooteghem J. C., Lambert de Rouvroit C., China B., Gustin A., Boudry P., Cornelis G. R. Analysis of virC, an operon involved in the secretion of Yop proteins by Yersinia enterocolitica. J Bacteriol. 1991 Aug;173(16):4994–5009. doi: 10.1128/jb.173.16.4994-5009.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  48. Michiels T., Wattiau P., Brasseur R., Ruysschaert J. M., Cornelis G. Secretion of Yop proteins by Yersiniae. Infect Immun. 1990 Sep;58(9):2840–2849. doi: 10.1128/iai.58.9.2840-2849.1990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Miller V. L., Mekalanos J. J. A novel suicide vector and its use in construction of insertion mutations: osmoregulation of outer membrane proteins and virulence determinants in Vibrio cholerae requires toxR. J Bacteriol. 1988 Jun;170(6):2575–2583. doi: 10.1128/jb.170.6.2575-2583.1988. [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Mills D. M., Bajaj V., Lee C. A. A 40 kb chromosomal fragment encoding Salmonella typhimurium invasion genes is absent from the corresponding region of the Escherichia coli K-12 chromosome. Mol Microbiol. 1995 Feb;15(4):749–759. doi: 10.1111/j.1365-2958.1995.tb02382.x. [DOI] [PubMed] [Google Scholar]
  51. Ménard R., Sansonetti P. J., Parsot C. Nonpolar mutagenesis of the ipa genes defines IpaB, IpaC, and IpaD as effectors of Shigella flexneri entry into epithelial cells. J Bacteriol. 1993 Sep;175(18):5899–5906. doi: 10.1128/jb.175.18.5899-5906.1993. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Ménard R., Sansonetti P., Parsot C. The secretion of the Shigella flexneri Ipa invasins is activated by epithelial cells and controlled by IpaB and IpaD. EMBO J. 1994 Nov 15;13(22):5293–5302. doi: 10.1002/j.1460-2075.1994.tb06863.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  53. Platt M. W., Miller K. J., Lane W. S., Kennedy E. P. Isolation and characterization of the constitutive acyl carrier protein from Rhizobium meliloti. J Bacteriol. 1990 Sep;172(9):5440–5444. doi: 10.1128/jb.172.9.5440-5444.1990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  54. Rawlings M., Cronan J. E., Jr The gene encoding Escherichia coli acyl carrier protein lies within a cluster of fatty acid biosynthetic genes. J Biol Chem. 1992 Mar 25;267(9):5751–5754. [PubMed] [Google Scholar]
  55. Sansonetti P. J. Molecular and cellular biology of Shigella flexneri invasiveness: from cell assay systems to shigellosis. Curr Top Microbiol Immunol. 1992;180:1–19. doi: 10.1007/978-3-642-77238-2_1. [DOI] [PubMed] [Google Scholar]
  56. Sasakawa C., Komatsu K., Tobe T., Suzuki T., Yoshikawa M. Eight genes in region 5 that form an operon are essential for invasion of epithelial cells by Shigella flexneri 2a. J Bacteriol. 1993 Apr;175(8):2334–2346. doi: 10.1128/jb.175.8.2334-2346.1993. [DOI] [PMC free article] [PubMed] [Google Scholar]
  57. Shearman C. A., Rossen L., Johnston A. W., Downie J. A. The Rhizobium leguminosarum nodulation gene nodF encodes a polypeptide similar to acyl-carrier protein and is regulated by nodD plus a factor in pea root exudate. EMBO J. 1986 Apr;5(4):647–652. doi: 10.1002/j.1460-2075.1986.tb04262.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  58. Stanley P., Packman L. C., Koronakis V., Hughes C. Fatty acylation of two internal lysine residues required for the toxic activity of Escherichia coli hemolysin. Science. 1994 Dec 23;266(5193):1992–1996. doi: 10.1126/science.7801126. [DOI] [PubMed] [Google Scholar]
  59. Straley S. C., Skrzypek E., Plano G. V., Bliska J. B. Yops of Yersinia spp. pathogenic for humans. Infect Immun. 1993 Aug;61(8):3105–3110. doi: 10.1128/iai.61.8.3105-3110.1993. [DOI] [PMC free article] [PubMed] [Google Scholar]
  60. Van Gijsegem F., Gough C., Zischek C., Niqueux E., Arlat M., Genin S., Barberis P., German S., Castello P., Boucher C. The hrp gene locus of Pseudomonas solanacearum, which controls the production of a type III secretion system, encodes eight proteins related to components of the bacterial flagellar biogenesis complex. Mol Microbiol. 1995 Mar;15(6):1095–1114. doi: 10.1111/j.1365-2958.1995.tb02284.x. [DOI] [PubMed] [Google Scholar]
  61. Venkatesan M. M., Buysse J. M., Oaks E. V. Surface presentation of Shigella flexneri invasion plasmid antigens requires the products of the spa locus. J Bacteriol. 1992 Mar;174(6):1990–2001. doi: 10.1128/jb.174.6.1990-2001.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  62. Voetz M., Klein B., Schell J., Töpfer R. Three different cDNAs encoding acyl carrier proteins from Cuphea lanceolata. Plant Physiol. 1994 Oct;106(2):785–786. doi: 10.1104/pp.106.2.785. [DOI] [PMC free article] [PubMed] [Google Scholar]
  63. Wei Z. M., Beer S. V. HrpI of Erwinia amylovora functions in secretion of harpin and is a member of a new protein family. J Bacteriol. 1993 Dec;175(24):7958–7967. doi: 10.1128/jb.175.24.7958-7967.1993. [DOI] [PMC free article] [PubMed] [Google Scholar]
  64. Wei Z. M., Laby R. J., Zumoff C. H., Bauer D. W., He S. Y., Collmer A., Beer S. V. Harpin, elicitor of the hypersensitive response produced by the plant pathogen Erwinia amylovora. Science. 1992 Jul 3;257(5066):85–88. doi: 10.1126/science.1621099. [DOI] [PubMed] [Google Scholar]
  65. Woestyn S., Allaoui A., Wattiau P., Cornelis G. R. YscN, the putative energizer of the Yersinia Yop secretion machinery. J Bacteriol. 1994 Mar;176(6):1561–1569. doi: 10.1128/jb.176.6.1561-1569.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  66. Yao R., Palchaudhuri S. Nucleotide sequence and transcriptional regulation of a positive regulatory gene of Shigella dysenteriae. Infect Immun. 1992 Mar;60(3):1163–1169. doi: 10.1128/iai.60.3.1163-1169.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  67. Zierler M. K., Galán J. E. Contact with cultured epithelial cells stimulates secretion of Salmonella typhimurium invasion protein InvJ. Infect Immun. 1995 Oct;63(10):4024–4028. doi: 10.1128/iai.63.10.4024-4028.1995. [DOI] [PMC free article] [PubMed] [Google Scholar]
  68. von Heijne G. A new method for predicting signal sequence cleavage sites. Nucleic Acids Res. 1986 Jun 11;14(11):4683–4690. doi: 10.1093/nar/14.11.4683. [DOI] [PMC free article] [PubMed] [Google Scholar]

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