Retroviral “terminal deoxynucleotidyl transferase” activity is reverse transcription

Abstract

Detergent-disrupted preparations of murine mammary tumor virus (MuMTV), Mason-Pfizer monkey virus (MP-MV), and Rauscher murine leukemia virus (RLV) were all found to be capable of catalyzing poly(dT) synthesis when only the exogenous primer oligo(dT) was supplied. Analysis of this apparent terminal deoxynucleotidyl transferase (TdT)-like DNA polymerase activity revealed that: (a) Optimal concentrations of divalent cations and the effect of KCl addition were similar or identical to those observed for reverse tranacriptase activity; (b) sensitivity to inhibition by inorganic phosphate for both TdT-like and reverse tranacriptase activity were identical and virion specific; (c) sedimentation coefficients obtained for TdT-like and reverse tranacriptase activity from each virion were identical, although almost all TdT-like activity was lost following velocity sedimentation of solubilized virions; the TdT-like activity could be restored through the addition of 70S RNA to reaction mixtures; (d) the products of TdT-like and reverse transcriptase reactions were found to be equally sensitive to S 1 nuclease treatment. Disruption of viral cores through the use of the ionic detergent sodium deoxycholate rendered TdT-like activity almost completely sensitive to RNase treatment. Additionally, antisera prepared against MP-MV DNA polymerase inhibited both TdT-like and reverse transcriptase activity to an identical degree. Our results therefore suggest that the “TdT” observed in MuMTV, MP-MV, and RLV is actually reverse tranacriptase activity directed by endogenous virion poly(A) annealed to the exogenously provided oligo(dT) primer.