Role of glutamine 151 of human immunodeficiency virus type-1 reverse transcriptase in substrate selection as assessed by site-directed mutagenesis

A natural mutation at codon 151 (Gln --> Met; Q151M) of HIV-I RT has been s hown to confer resistance to the virus against dideoxy nucleoside analogues [Shirasaka, T., et al. (1995) PI-oc. Natl. Acad Sci. U.S.A. 92, 2398], sug gesting that Gin 151 may be involved in conferring sensitivity to nucleosid e analogues, To understand its functional implication, we generated two mut ant derivatives of this residue (Q151M and Q151N) and examined their sensit ivities to ddNTPs and their ability to discriminate against rNTPs versus dN TP substrates on natural U5-PBS HIV-I RNA template. We found that Q151M was highly discriminatory against all four ddNTPs but was able to incorporate rNTPs as efficiently as the wild type enzyme. In contrast, the Q151N mutant was only moderately resistant to ddNTPs but exhibited a higher level of di scrimination against rNTPs, The fidelity of misinsertion was found to be hi ghest for the Q151N mutant followed by Q151M and the wild type enzyme. Thes e results point toward the importance of the amino acid side chain at posit ion 151 in influencing the ability of the enzyme in recognition and discrim ination against the sugar moieties of nucleotide substrates.