SELECTIVE ACTION OF 4'-AZIDOTHYMIDINE TRIPHOSPHATE ON REVERSE-TRANSCRIPTASE OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 AND HUMAN DNA POLYMERASE-ALPHA AND POLYMERASE-BETA

4'-Azidothymidine (ADRT) is a novel nucleoside analogue that exhibits potent inhibitory activity against the replication of human immunodefi ciency virus (HIV) in lymphocytes. The mechanisms by which ADRT inhibi ts HIV reverse transcriptase (HIV-RT) as ADRT 5'-triphosphate (ADRT-TP ), the active intracellular metabolite of ADRT, and as the ADRT-MP mol ecule incorporated into DNA were examined and compared to their effect s on human DNA polymerases alpha and beta. Inhibition of HIV-RT by ADR T-TP is competitive against TTP and is more potent against RNA to DNA synthesis (K(i) = 0.009 muM versus K(m) = 3.3 muM for TTP) than it is against DNA to DNA synthesis (K(i) = 0.95 muM versus K(m) = 16.3 muM f or TTP). ADRT-TP is also a more potent inhibitor for primer elongation on RNA template than on DNA template. ADRT-TP is a poor inhibitor of human DNA polymerases alpha (K(i) = 62.5 muM) and beta (K(i) = 150 muM ) (Chen et al., 1992). The consequences of ADRT incorporation into DNA are strikingly different for the HIV-RT and for human DNA polymerases alpha and beta. DNA polymerases alpha and beta incorporate a single A DRT-MP molecule into nascent DNA at a very slow rate and continue to e longate. They are unable to incorporate a second consecutive ADRT-MP. However, HIV-RT is able to efficiently incorporate two consecutive ADR T molecules. Incorporation of two consecutive ADRT-MP molecules by HIV -RT prevents further DNA chain elongation. Incorporation of two ADRT-M P molecules separated by one deoxyribonucleoside monophosphate (dAMP, dCMP, or dGMP) also abolishes DNA chain elongation by HIV-RT.