The early
DNa products of reverse transcription have been analyzed from reconstructed reactions containing avian myeloblastosis virus 35S
RNA .
tRNAtrp complex and highly purified
reverse transcriptase. We describe conditions for the synthesis of genome-length
complementary DNA and two discrete species of plus strand
DNA (the same chemical polarity as the
viral RNA genome) about 300 and 400
nucleotides in length. Plus DNA400 and plus DNA300 were detected by molecular hybridization with
DNA probes complementary to sequences from both the 3'- and 5'-ends of the
viral RNA. Both species appear to be copied from the 5'-end of minus strand
DNA by their hybridization properties and their early synthesis when only the 5'-end of minus strand
DNA is available as template.
Restriction endonuclease mapping of plus DNA400 and plus DNA300 rules out a precursor-product relationship between the two. Rather the results suggest a unique initiation site for both species, with plus DNA400 containing internal sequences not present in plus DNA300. Plus DNA400 and plus DNA300 appear to be analogous to early plus
DNA species detected in cells early after
retrovirus infection. Thus, purified
reverse transcriptase appears to be enzymatically sufficient for synthesis of genome-length
complementary DNA and initiation and synthesis of early plus strand
DNA as observed in infected cells.