The establishment of a genetic map of orf virus reveals a pattern of genomic organization that is highly conserved among divergent poxviruses.

The large differences between the G+C content of the orf virus genome and those of other characterized poxviruses have precluded the use of DNA hybridization to establish a gene map of orf virus. Here we have sequenced the ends of cloned restriction endonuclease fragments of the nZ2 strain of orf virus (OV) and used the translated sequences to search protein data bases. Sequence from 15 points found high-scoring matches to data base entries, including 18 vaccinia virus (VAC) genes. We also present 2 kb of sequence from a region near the right terminus of the OV genome and show that it encodes homologs of VAC genes, F9L and F10L. The data presented here in conjunction with published and as yet unpublished data have allowed the construction of a gene map of OV on which 37 genes have been placed. Thirty-two of these genes have homologs in VAC. Alignment of the OV gene map with that of VAC revealed that each OV gene and its VAC counterpart occurred in the same order and orientation on their respective genomes. The intervals between many of the points of sequence were also found to be strikingly similar. The conserved spacing of genes between OV and VAC within the central 88.2 kb of the 139-kb OV genome is not maintained in the termini where insertion, deletion, and translocation have occurred. Parallels are drawn between the data presented here and related data from swinepox virus and capripox virus.