Unintegrated and integrated proviruses of two strains of baboon endogenous viruses: Comparative restriction endonuclease analysis

Abstract

We have deduced restriction enzyme maps of 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 cuts within 400 nucleotides from both ends of the linear form. However, the cleavage sites for BamHI, SalI, and BclI are distinguishable for the two virus genomes. In addition to the linear 455K proviral DNA molecules which contain a direct terminal repeat of 0.6 ± 0.2 kolobases, two discrete species of circular proviral intermediates were also detected. One corresponds in size to the linear viral DN molecules and the other has a deletion of 600 base pairs mapping in the region of the 3′-5′ joint XhoI fragment. This deletion is probably equivalent to one unit of large terminal repeat sequences (LTR). We also examined the integrated proviruses in heterologous cells infected with M7 and 455K. The results indicate that the integrated proviruses are colinear with the virus genomes and retain both copies of LTR. The sites of integration are multiple in uncloned cells. Two cell clones examined carry three to five proviruses. These results are similar to previous studies of other integrated retroviruses. They also provide a comparative basis for examining the organization and divergence of the endogenous baboon virogenes in different primates. Those studies are presented in the accompanying paper.