DNA Sequence Relationship of the Baboon Endogenous Virus Genome to the Genomes of Other Type C and Type D Retroviruses

Abstract

Baboon endogenous virus (BaEV) is a type C retrovirus present in multiple proviral copies in the DNA of baboons. Although interspecies antigenic determinants present on reverse transcriptase and gag proteins are shared among all mammalian type C viruses, no nucleic acid homology between BaEV and other type C viruses (except RD-114) was found in conventional liquid hybridization experiments. Restriction fragments of cloned BaEV DNA immobilized on nitrocellulose were used to test for relatedness with [32P]c[complementary]DNA of various type C and type D viruses. The following distant relationships previously found only through immunological and protein sequencing techniques were detected: 8 type C viral cDNA (the endogenous virus of rhesus monkeys, feline leukemia virus, simian sarcoma virus, gibbon ape leukemia virus, Rauscher murine leukemia virus, BALB-2, NZB and RD-114) and 2 type D viral cDNA (Mason-Pfizer monkey virus and squirrel monkey retrovirus) were able to hybridize with cloned BaEV DNA; the 8 type C probes hybridized to restriction fragments spanning most of the BaEV genome, but only RD-114 hybridized to fragments within the 1.9 kilobases at the 3'' end of the genome; the 2 type D probes hybridized primarily to fragments within the 1.9 kilobases at the 3'' terminus and weakly or not all elsewhere; and [32P]cDNA of several other oncornaviruses (mouse mammary tumor virus, equine infectious anemia virus, bovine leukemia virus and reticuloendotheliosis virus) exhibited no homology with BaEV DNA. DNA sequence analysis allowed orientation of the BaEV restriction map with the genetic map at both ends of the genome. Homologies between retroviral cDNA and BaEV clone restriction fragments could thus be related to specific BaEV genes. Whereas type C cDNA hybridized to fragments from gag, pol and the pol-env junction, squirrel monkey retrovirus cDNA hybridized only to a fragment coding for the p15E portion of env. Mason-Pfizer monkey virus cDNA also hybridized within the p15E region but exhibited homology to the 3'' half of gp70 as well. These results are discussed relative to previously reported antigenic relatedness of retroviral proteins. BaEV apparently represents an important link in oncornavirus evolution.