Specific binding of tryptophan transfer RNA to avian myeloblastosis virus RNA dependent DNA polymerase (reverse transcriptase)

The ability of tryptophan tRNA (tRNA(Trp)) to initiate reverse transcription of the 70S RNA of avian RNA tumor viruses suggested that the reverse transcriptase (RNA dependent DNA polymerase; deoxynucleosidetriphosphate: DNA deoxynucleotidyltransferase; EC 2.7.7.7) might have a specific binding site for the tRNA. A complex of tRNA(Trp) and the avian myeloblastosis virus reverse transcriptase has been demonstrated using chromatography on Sephadex G100 columns. Of all the chicken tRNA's only tRNA(Trp) and a tRNA₄(Met) bind to the enzyme with high enough affinity to be selected from a mixture of the chicken cell tRNAs. The ability of tRNA(trp) to change the sedimentation rate of the enzyme indicates that tRNA(Trp) is not binding to a concomitant in the enzyme preparation. Treatment of the enzyme with monospecific antibody to reverse transcriptase prevented binding of tRNA as well as inhibited the DNA polymerase activity of the enzyme. The ability of reverse transcriptase to utilize tRNA(Trp) as a primer for DNA synthesis, therefore, appears to involve a highly specific site on the enzyme.