TAT IS REQUIRED FOR EFFICIENT HIV-1 REVERSE TRANSCRIPTION

The ability of human immunodeficiency virus-1 (HIV-1) to undergo effic ient reverse transcription is dependent on a number of parameters, The se include the binding of the tRNA(3)(Lys) to the HIV-1 primer binding site and the subsequent interaction with the heterodimeric reverse tr anscriptase. Recently, we demonstrated that TAR RNA was also necessary for efficient HIV-1 reverse transcription, Given the fact that the Ta t protein is involved in the activation of HIV-1 gene expression in co njunction with TAR, we wished to determine whether Tat might also be i nvolved in the control of HIV-1 reverse transcription. HIV-1 virions d eleted in the tnt gene were unable to initiate reverse transcription e fficiently upon infection of peripheral blood mononuclear cells (PBMCs ), This defect was not due to decreased amounts of genomic RNA, revers e transcriptase or other HIV-1 proteins which were incorporated into t he virion, Following transfection of wild-type but not mutant tat gene s into cell lines producing HIV-1 lacking tat, the virions produced co uld be complemented for defects in reverse transcription upon subseque nt infection of PBMCs, In contrast, the defect in reverse transcriptio n seen with HIV-1 lacking the tat gene could not be complemented when the target cells rather than the producer cells contained tat, Viruses lacking tat were also defective in endogenous assays of reverse trans cription, although these viruses contained similar levels of reverse t ranscriptase. These results indicate that the Tat protein, in addition to regulating the level of gene expression, is also important for eff icient HIV-1 reverse transcription.