Characterization of the gene encoding the A-type inclusion protein of camelpox virus and sequence comparison with other orthopoxviruses.

A gene was identified in camelpox virus strain CP-1 that is similar to the 160K gene of cowpox virus strain Brighton (BR) that encodes the A-type inclusion body protein (ATIP). The CP-1 gene was mapped, sequenced, and the presence of the ATIP-specific mRNA was demonstrated. The open reading frame [2178 nucleotides (nt)] was found at a similar position in the CP genome as the one reported for the cowpox virus 160K ATI gene. DNA sequence comparison revealed a deletion of two adjacent adenine residues relative to cowpox virus BR, generating a reading frame shift accompanied by the formation of a translational stop codon. An identical deletion has been described for vaccinia virus strain Western Reserve. The DNA sequence of the corresponding region of monkeypox virus strain Copenhagen revealed a deletion leading to a putative stop codon 75 nt upstream of the same stop codons in the camelpox and vaccinia virus genes. These findings are consistent with the expression of truncated ATIPs, of 94K in vaccinia and camelpox viruses and of 92K in monkeypox virus. In addition, a deletion of 789 bp could be localized downstream of the ATI open reading frame in camelpox virus isolates of different origin. This causes the transcription of a shortened ATI-specific mRNA (3.7 kb) relative to vaccinia and cowpox viruses (both 4.5 kb). The similarity observed in ATIP-encoding and flanking sequences might suggest that vaccinia and camelpox viruses are descended from a common ancestor.