We have prepared DNA complementary to a sequence of 300-400 nucleotides adjacent to the poly(A) at the 3′-terminus of the genome of avian sarcoma virus (ASV) DNA was transcribed from denatured ASV RNA following initiation on the primer (dT)12-18. We demonstrated that homopolymer synthesis was not a significant feature of our enzymatic reaction, and we proved that most if not all the initiations on (dT)12-18 occurred at or near the 3'-terminus of the viral RNA. The presence of oligo(dT) on cDNA3, accelerates hybridization between cDNA3, and polyadenylated viral RNA; this artifact can be eliminated by including a competing homopolymer [poly(dT) or poly(A)l in the reaction mixtures. Nucleotide sequences complementary to cDNA3, occur only once or twice in the genome of avian sarcoma viruses, are present in the genomes of virus strains from subgroups A, B, C, D, E, and F of avian leukosis-sarcoma viruses, and are conserved even when large deletions affect an adjacent viral gene (src) By contrast, we find little or no complementarity between cDNA3, and the genomes of golden pheasant virus (subgroup G of avian leukosis-sarcoma viruses), mouse mammary tumor virus, and the Moloney strains of murine sarcoma virus and murine leukemia virus. cDNA3, can be used to identify the 3′-terminus of the avian sarcoma virus genome by molecular hybridization and will therefore be a useful reagent for the analysis of viral replication.
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