NEVIRAPINE ALTERS THE CLEAVAGE SPECIFICITY OF RIBONUCLEASE-H OF HUMAN-IMMUNODEFICIENCY-VIRUS-1 REVERSE-TRANSCRIPTASE

The action of the dipyridodiazepinone nevirapine (BI-RG-587) on polymerization and RNase H activities of human immunodeficiency virus reverse transcriptase (RT) was examined. Substrates using heteropolymeric DNA primers hybridized to complementary RNA templates were employed. Challenged assays were performed that allowed measurement of activity of the RT resulting from a single round of binding of RT to substrate. Results demonstrated that nevirapine alters the cleavage specificity of the RNase H. Instead of a primary cleavage approximately 18 nucleotides upstream of the DNA 3' terminus, multiple cleavages were observed ahead of and behind this site. This indicated that the compound facilitates sliding of the RT away from the DNA primer terminus allowing cleavage at more sites. The change in specificity occurred whether the primer terminus was at the end or internal on the template. Experiments with RNA primers on circular DNA demonstrated a nevirapine-induced stimulation of RNase H activity beyond the increase expected from the change in cleavage specificity. Examination of polymerization showed that the compound decreased both the number of primers that underwent synthesis and the processive elongation of those primers, The significance of these results with respect to viral replication and recombination is discussed.