Initiation of plus-strand DNA synthesis during reverse transcription of an avian retrovirus genome.

Two in vitro approaches were used to investigate the priming of strong-stop plus DNA by Rous sarcoma virus. This 340-base DNA species is the first major plus-strand DNA product seen in both infected cells and in endogenous reactions of disrupted virions. In the first approach, we set up a reconstructed system in which strong-stop plus DNA was synthesized by reverse transcriptase from a high-molecular-weight minus-strand viral DNA template. This synthesis was shown to be strictly dependent on the addition of primers to the reaction mixture. The addition of high-molecular-weight RNA from both viral and cellular sources, as well as oligodeoxyguanylate, gave specific synthesis of strong-stop plus DNA, whereas the addition of oligodeoxycytidylate-oligodeoxyadenylate and viral 4S RNA did not. In the second approach, strong-stop plus DNA synthesized in melittin-permeabilized virions was examined on a high-resolution polyacrylamide gel. This DNA was shown to have ca. 11 to 13 ribonucleotides at its 5' end. These results indicate that strong-stop plus DNA is initiated on a preformed RNA primer.