Synthesis, processing, and composition of the virion-associated HTLV-1 reverse transcriptase.

It is not known whether the low infectivity and low virion-associated polymerase activity of human T-cell lymphotropic virus type-1 (HTLV-1) are due to the quantity or quality of the reverse transcriptase (RT), because the protein has not yet been fully characterized. We have developed anti-RT antibodies and constructed HTLV-1 expression plasmids that express truncated or hemagglutinin-tagged Pol polyproteins to examine the maturation and composition of HTLV-1 RT. We detected virion-associated proteins corresponding to RT-integrase (IN) (pr98) and RT (p62) as well as smaller proteins containing the polymerase (p49) or RNase H domains. We have identified the amino acid sequences in the Pol polyprotein that are cleaved by HTLV-1 protease to yield RT and IN. We have also identified the cleavage sites within RT that give rise to the p49 polymerase fragment. Immunoprecipitation of an epitope-tagged p62 subunit coprecipitated p49, indicating that the HTLV-1 RT complex can exist as a p62/p49 heterodimer analogous to the RT of HIV-1 (p66/p51).