REVERSE-TRANSCRIPTASE AND SUBSTRATE DEPENDENCE OF THE RNA HYPERMUTAGENESIS REACTION

G-->A hypermutation is a remarkable phenomenon resulting from retrovir al reverse transcription in the presence of highly biased dNTP concent rations, Of the three reverse transcriptases (RTases) available, those of human immunodeficiency virus type 1 (HIV-1), avian myeloblastosis virus (AMV) and Moloney murine leukemia virus (MoMLV), the HIV-I enzym e showed the greatest sensitivity to biased [dCTP]/[dTTP] ratios. The HIV-1 RTase was able to discriminate between dUTP, dITP and the four D NA precursors and was insensitive to pH. There was little preference f or nucleotide contexts, A few exceptionally modified sequences were fo und presumably resulting from G-->A hypermutation and multiple strand transfer, This particular predilection of the HIV-1 and, by extrapolat ion, the lentiviral RTases towards G-->A hypermutation suggests that t he phenomenon may have contributed to the remarkably elevated A conten t of these retroviral genomes.