The DNAs of rabbitpox, vaccinia, Cowpox, ectromelia and fowl pox virus, all
grown in the same host system, were cleaved with restriction endonucleases
HindIII, BarnI and EcoRI. The resulting digestion products were separated by
electrophoresis on agarose slab gels. From the similarities and dissimilarities of
the migration profiles obtained, it was concluded that vaccinia and rabbitpox virus
are genetically the most closely related viruses investigated, although their DNA
cleavage patterns are clearly distinguishable. Cowpox and ectromelia virus both
show about the same degree of relatedness to each other as to rabbitpox and
vaccinia virus. Fowl pox virus, which belongs to the genus Avipoxvirus, contains
the largest genome examined (approx. I6O × IO
6 daltons) and the cleavage patterns
of its DNA show no similarities with those of orthopoxvirus DNAs, thus indicat-
ing a very low degree of genetic relatedness. We believe that restriction analysis is
a useful method for the identification and classification of poxvirus isolates.