Interaction of Tryptophan tRNA and Avian Myeloblastosis Virus Reverse Transcriptase: Further Characterization of the Binding Reaction

The interaction between the RNA tumor virus reverse transcriptase and the tRNA primers that initiate DNA synthesis has been studied. The binding of tRNA^Trp by avian myeloblastosis virus (AMV) reverse transcriptase is not strongly influenced by ionic strength or the presence of divalent cations. The enzyme will not bind fragments of tRNA^Trp produced by cleavage at the anticodon loop or at the m⁷G residue suggesting that much of the tRNA structure is required for effective binding. However, tRNA^Trp modified in various ways at its 3′-OH end is bound, indicating that that end of the molecule is not crucial to the binding. The α subunit of the AMV reverse transcriptase does not detectably bind tRNA^Trp nor does the subunit transcribe AMV 70S RNA efficiently. The AMV holoenzyme efficiently transcribes both Rous sarcoma virus (RSV) and Moloney murine leukemia virus (M-MuLV) 70S RNAs. tRNA^Trp is the primer used when the AMV enzyme transcribes the RSV template, while tRNA^Pro is the primer used when the AMV enzyme transcribes the M-MuLV template. The M-MuLV reverse transcriptase copies M-MuLV, AMV, and RSV 70S RNAs efficiently. However, M-MuLV reverse transcriptase does not tightly bind tRNA^Pro or tRNA^Trp.