Recognition of 2'-deoxy-l-ribonucleoside 5'-triphosphates by human telomerase

Telomerase is classified as one of the reverse transcriptases (RTs). To clarify whether l-enantiomers of natural 2'-deoxyribonucleoside 5'-triphosphates (dNTPs) are recognized by human telomerase, a quantitative telomerase assay based on the "stretch PCR" method was developed and used for kinetic analysis of the inhibitory effects of these compounds on the enzyme. Among the four l-enantiomers of dNTPs, l-dTTP and l-dGTP inhibited telomerase activity and the others showed slight or no inhibitory effect. Lineweaver-Burk plot analysis showed that the inhibition modes of l-dTTP and l-dGTP were partially competitive (mixed type) and competitive with the corresponding substrate dNTP, respectively. However, the K(i) values of l-dTTP and l-dGTP (21 and 15 microM) were several times larger than the K(m) values (3-6 microM). These results suggest that the active site of telomerase is not able to discriminate strictly the chirality of dNTPs, although it is more discriminatory than HIV-1 RT.