SUBUNIT SPECIFICITY OF MUTATIONS THAT CONFER RESISTANCE TO NONNUCLEOSIDE INHIBITORS IN HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 REVERSE-TRANSCRIPTASE

We constructed plasmid vectors that simultaneously express both the p6 6 and p51. subunits of human immunodeficiency virus type 1 (HIV-1) rev erse transcriptase (RT) in Escherichia coli. These vectors allow us to generate HIV-1 RT heterodimers in which either the p66 or the p51 sub unit has the wild-type sequence and the other subunit has a specific a mino acid substitution. We used these vectors to express HIV-1 RT hete rodimers containing several different amino acid substitutions reporte d to confer resistance to nonnucleoside inhibitors. Most of the amino acid substitutions conferred resistance to nonnucleoside inhibitors R8 6183 (TIBO) and TSAO-m(3)T only when present in the p66 subunit of the p66-p51 heterodimer; heterodimers that contained a wild-type p66 subu nit and a mutant p51 subunit remained sensitive to the inhibitors. How ever, there was one mutation, E138K, that conferred drug resistance wh en the mutation was present in the p51 subunit. The corresponding hete rodimer with the E138K mutation in the p66 subunit and a wild-type p51 subunit remained sensitive to the inhibitors. Analysis of the three-d imensional structure of HIV-1 RT indicated that residue 138 of the p51 subunit is in the nonnucleoside inhibitor-binding pocket while residu e 138 of the p66 subunit is not. The mutagenesis results, combined wit h structural data, support the idea that the nonnucleoside inhibitors exert their effects by binding to a hydrophobic pocket in the RT heter odimer and that mutations which give rise to drug resistance directly interfere with the interactions between the nonnucleoside inhibitors a nd HIV-1 RT.