FIG 7.

A26 is conserved in chordopoxviruses with the exception of arthropod-transmitted clade II chordopoxviruses. Occurrence of the indicated loci in established poxvirus genera. Genes with significant homology present in a genus are denoted by filled black rectangles; gray rectangles indicate extraneous nonhomologous sequence. The A24 and A28 genes immediately flank the virus differentiation locus in chordopoxviruses. The F13 EV-associated gene is separated from the differentiation locus by ∼100 kb in chordopoxviruses, depending on the genus. The A25/A26 differentiation system is present in virtually all known clade I chordopoxviruses (excluding crocodylidviruses) and absent in all known clade II chordopoxviruses. Parapoxviruses lack the A25 gene but have two nonidentical A26 homologs in tandem. Molluscipoxviruses have two A26 homologs and an intervening unrelated ORF. Molluscipoxviruses, avipoxviruses, and crocodylidviruses lack A27. Crocodylidviruses lack A25 and have a longer, weakly homologous ORF in lieu of A26. Entomopoxviruses lack the F13 gene as well as the A25/A26 differentiation locus, which is replaced by several ORFs showing no homology; Alphaentomopoxviruses have A24 and A28 swapped. Phylogenetic distances are not to scale, and virus genera are arranged according to phylogeny of the E9 DNA polymerase gene.