Effect of viral RNase H on the avian sarcoma viral genome during early transcription in vitro.

We investigated the influence of viral RNase H on the transcription of the avian sarcoma virus RNA in a virion-associated reaction. The ability of RNase H to degrade the RNA moiety of the initially formed RNA-DNA hybrid at the 5' end of the viral genome was found to be greatly dependent on the exact concentration of nonionic detergent used to activate the reaction. At a detergent concentration optimal for extensive and faithful in vitro transcription of avian sarcoma virus RNA by the virion-associated RNA-dependent DNA polymerase, most of the 5' terminus of the RNA was digested in 30 min at 41 degrees C. At higher than optimal detergent concentrations, however, little of that RNA was digested. We conclude that removal of the 5'-terminal redundancy in the RNA after its transcription into DNA is a prerequisite for base pairing of the DNA to the 3'-terminal redundant sequence. Lack of removal of this sequence leads to incorrect elongation and substantial reduction of DNA synthesis. When tested with a synthetic RNA-DNA hybrid, virion-associated RNase H did not reveal a detergent dependence.