Purification of DNA complementary to the env gene of avian sarcoma virus and analysis of relationships among the env genes of avian leukosis sarcoma viruses

The env gene of avian leukosis sarcoma viruses encodes a glycoprotein that determines the host range and surface antigenicity of virions. We have purified radioactive DNA (cDNA(gp)) complementary to at least a portion of the env gene for viral subgroups A and C; complementary DNA was synthesized with purified virions of wild type avian sarcoma virus, and RNA from a mutant with a deletion in env was used to select DNA specific to env by molecular hybridization. The genetic complexity of cDNA(gp) for subgroup A (ca. 2,000 nucleotides) was sufficient to represent the entire deletion and most or all of the env cistron. The deletions in env in two independently isolated strains of virus (Bryan and rdNY8SR) overlap, and cDNA(gp) represents nucleotide sequences common to both deletions. By contrast, we could detect no overlap between deletions in nv and deletions in the adjacent viral gene src. Laboratory stocks of viral subgroups A, B, C, D, and E do not contain detectable amounts of env deletions when tested by molecular hybridization; hence, segregation of deletions in env is a less frequent event than the segregation of deletions in the viral transforming gene src (Vogt, 1971). We found extensive homology among the nucleotide sequences encoding the env genes of virus strains indigenous to chickens (subgroups A, B, C, D, and E), although subgroups B, D and E appear to differ slightly from subgroups A and C at the env locus. By contrast, viruses obtained from pheasant cells (subgroups F and G) have env genes with little or no relationship to env genes of chicken viruses. According to available data, viruses of subgroup F arose by recombination between an avian sarcoma virus viral genes in the genome of ring necked pheasants, whereas subgroup G viruses may be entirely endogenous to golden pheasants.