Nucleotide sequence comparison of homologous genomic regions from variola, monkeypox, and vaccinia viruses

The nucleotide sequences of homologous regions from the genomes of variola major strain Harvey, variola minor strains Butler and Garcia, and monkeypox strain Denmark were determined. The nucleotide sequences were compared to the homologous region in vaccinia virus which contains part of one of the genes involved in determining host range. Two major differences were detected; these corresponded to a deletion in the promoter region and the presence of a premature stop codon. It was concluded that this region of the genome may not be actively expressed in either variola- or monkeypox-virus-infected cells. It was also concluded that diagnostic nucleic acid hybridisation probes for differentiating between these members of the Orthopoxviridae may be difficult to identify.