BABOON ENDOGENOUS VIRUS GENOMES IN OLD WORLD PRIMATES: EVIDENCE FOR INFECTION POSTSPECIATION

Restriction enzyme maps were determined for the unintegrated DNA of two strains of baboon endogenous virus, 455K and M7. These were isolated from two closely related species, Papio anubis and Papio cynocephalus. Of the seven restriction enzymes used, EcoRI, HindIII, PvuII, and XhoI gave conserved cleavage patterns for both genotypes. XhoI cleaved within 400 nucleotides from both ends of the linear forms. However, the cleavage sites for BamHI, SalI, and BclI were indistinguishable for the two virus genomes. In addition to the linear 455K proviral DNA molecules which contained a direct terminal repeat of 0.6 (+OR-) 0.2 kilobases, two discrete species of circular proviral intermediates were also detected. One corresponded in size to the linear viral DNA molecules, and the other had a deletion of 600 base pairs which mapped in the region of the 3'-5' joint XhoI fragment. This deletion is probably equivalent to one unit of large terminal repeat sequences (LTR). Examination of the integrated proviruses in heterologous cells infected with M7 and 455K showed their integration to be colinear with the unintegrated linear viral genomes and that the proviruses retained both copies of LTR. The sites of integration were multiple in uncloned cells. Cloned cells were examined and found to contain three to five proviruses. Comparative restriction endonuclease analysis of BaEV DNA in Asian and African species of Old World monkeys revealed at least two classes of virogenes; one class includes genotypes found among all Old World monkeys with no apparent correlation to their phylogeny or geographical habitat. These either represent virogenes that were introduced early before speciation of the Old World monkey or proviruses of a more recent widespread infection. Another class contains genotypes that are distinct for African and Asian primates. Instead of a more rapid "divergence" of BaEV genes in Asian primates as previously proposed, these data are more consistent with prevalence of different strains of BaEV of this class in different geographical areas.