Mutants of the Rous sarcoma virus reverse transcriptase gene are nondefective in early replication events.

The functional domains of the avian retrovirus polymerase gene are at least tripartite in nature. Three enzymatic domains exist; the RNase H and DNA polymerase activities are located on the alpha subunit while the DNA endonuclease is located on the pp32 moiety. Virus mutants possessing deletions in the pp32 region demonstrated that this region encodes function(s) essential for replication of the virus while separate point mutations generated near the NH2 terminus of pp32 resulted in decreased replication and cell transformation. Molecular analysis of various steps in the virus replication cycle demonstrated that the synthesis of linear viral DNA, transport of viral DNA to the nucleus, and its subsequent circularization and integration into cellular DNA are apparently not affected in these point mutants. However, the synthesis of viral RNA from the integrated provirus of these point mutants appears less than that observed in wild type virus-infected cells. What role the mutated pp32 protein might have on viral transcription is discussed.