Synthesis of murine leukemia virus plus strong stop DNA initiates at a unique site.

The 5'-terminal segment of plus strong stop DNA has been isolated from an endogenous virion reverse transcription reaction and characterized. The plus strong stop DNA is shown to initiate with the sequence 5'AATGAAAGA.... The 5'-terminal nucleotide is a deoxyribonucleotide. No residual protein or RNA moiety was found attached to the plus strong stop DNA. Thus, the mechanism which primes plus strand synthesis is still unclear. No evidence for multiple initiation sites or heterogeneous starts is observed. This data indicates that the initiation of plus strong stop DNA synthesis by the virion RNA-dependent DNA polymerase is a precise event which occurs at a unique site on the retrovirus genome.