Second-site reversion of a human immunodeficiency virus type 1 reverse transcriptase mutant that restores enzyme function and replication capacity

Nonconservative substitutions for Tyr-115 in the reverse transcriptase (RT) of human immunodeficiency virus type 1 (HIV-1) lead to enzymes displaying lower affinity for deoxynucleoside triphosphates (dNTPs) (A. M. Martin-Hern andez, E. Domingo, and L. Menendez-Arias, EMBO J. 15:4434-4442, 1996). Seve ral mutations at this position (Y115W, Y115L, Y115A, and Y115D) were introd uced in an infectious HIV-1 clone, and the replicative capacity of the muta nt viruses was monitored. Y115W was the only mutant able to replicate in MT -4 cells, albeit very poorly. Nucleotide sequence analysis of the progeny v irus recovered from supernatants of four independent transfection experimen ts showed that the Y115W mutation was maintained. However, in all cases an additional substitution in the primer grip of the RT (M230I) emerged when t he virus increased its replication capacity. Using recombinant HIV-1 RT, we demonstrate that M230I mitigates the polymerase activity defect of the Y11 5W mutant, by increasing the dNTP binding affinity of the enzyme. The secon d-site suppressor effects observed were mediated by mutations in the 66-kDa subunit of the RT, as demonstrated with chimeric heterodimers. Examination of available crystal structures of HIV-1 RT suggests a possible mechanism for restoration of enzyme activity by the second-site revertant.