The 2',3'-dideoxynucleoside triphosphates (
ddNTPs) are potent substrate analog inhibitors of human immunodeficiency virus (
HIV) reverse transcriptase and have clinical utility in the treatment of
acquired immunodeficiency syndrome. Several issues regarding the interaction of these compounds with
HIV reverse transcriptase were examined. The potency of unsubstituted
ddNTPs and the 3'-azido analog of
dTTP (
AZTTP) was influenced by the choice of template. Both compounds were more potent with the complementary homopolymer templates than with gapped duplex
DNA, although the Km for the competing dNTP was similar with different templates. The Ki for
AZTTP was greater than for the unsubstituted
ddNTPs with either a homopolymer or a gapped duplex
DNA template.
HIV reverse transcriptase incorporated ddCMP and
AZTMP into primed phage m13
DNA at sites specified for insertion of
dCMP and
dTMP, respectively. ddCTP was more efficiently utilized as a substrate than was
AZTTP. Primer elongation due to base misincorporation was observed in the absence of one dNTP. The combined effect of
ddNTPs and the
pyrophosphate analog phosphonoformate (PFA) on
HIV reverse transcriptase was also examined, and inhibition by PFA in combination with
ddTTP or
AZTTP was mutually exclusive.