Classification of herpesvirus saimiri into three groups based on extreme variation in a DNA region required for oncogenicity.

The leftmost 7 kilobase pairs of unique sequence L-DNA of herpesvirus saimiri was found to be highly variable among different strains as determined by restriction endonuclease analysis and blot hybridization. This region in one group of viruses (group A) showed only very weak hybridization with the DNA of two other groups. Similarly, a fragment of group B hybridized to DNA of its own group much more strongly than to group A. No homology was detected within a 1.2-kilobase-pair region between strain 11 (group A virus) and strain SMHI (group B) even under reduced stringency, and the adjacent 5.5-kilobase-pair segment of the region showed only a very weak intergroup hybridization. DNA of a third group of viruses (non-A, non-B) did not hybridize significantly with cloned fragments representing the leftmost 7-kilobase-pair region of either group A or group B. Since sequences in the highly variable region are required for the oncogenicity of the virus, these results raise interesting questions regarding the origin and function of this region of the genome.