Mechanism of release of the avian retrovirus tRNA Trp primer molecule from viral DNA by ribonuclease H during reverse transcription

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Employing enzymatic reactions containing reverse transcriptase and appropriately defined substrates, we have demonstrated that the tRNA Trp primer molecule required for the initiation of DNA synthesis is cleaved from viral DNA by an enzymatic activity associated with the reverse transcriptase molecule. Since the α subunit of reverse transcriptase facilitates release of the tRNA Trp primer from viral DNA and this activity is inhibited by a known inhibitor of reverse-transcriptase-associated RNAase H, it appears that the RNAase H activity, rather than the DNA endonuclease activity, is involved in this reaction. The cleavage site for RNAase H—mediated removal of the tRNA Trp primer from viral DNA is located at or near the tRNA Trp—viral DNA junction, and transcription of most, if not all, of the tRNA Trp-binding site into (+) polarity DNA occurs before RNAase-H—mediated cleavage takes place. These studies indicate that an additional function can be ascribed to the reverse-transcriptase-associated RNAase H activity, which in this instance acts like an endonuclease, not requiring the unblocked termini of an RNADNA hybrid molecule for its activity.