Polymerase-defective mutant of the bryan high-titer strain of Rous sarcoma virus

A mutant of the Bryan high-titer strain of Rous sarcoma virus defective in reverse transcriptase is known as type alpha (BH-RSV alpha). BH-RSV alpha virion particles do not contain any polymerse-related proteins but they direct the synthesis of a normal sized Prl80 gag-pol polyprotein precursor in infected cells. Using a bioassay for polymerase gene function that is based on the requirement of viral replication for transformation of transfected chicken cells, we have localized the defect to the 2.5 kb EcoRI-KpnI DNA fragment containing more than 90% of the polymerase gene by comparison with the corresponding DNA fragment from the wild-type polymerase-positive BH-RSV, called type beta. In vitro recombination experiments with the polymerase gene of Schraidt-Ruppin RSV allowed us to map the defect to the 0.86 kb Xbal-BglII DNA fragment of the BH-RSV alpha polymerase. DNA sequence analysis of the entire polymerase gene of BH-RSV alpha and beta hasrevealed one point mutation that maps within that XbaI-BglII fragment and substitutes leucine in BH-RSV alpha for glutamine in the wild-type BH-RSV beta.