Drug susceptibility measurements obtained with recombinant HIV-1 clones containing RTs M41L/Δ67/T69G/K70R/T215Y, M41L/S68G/Δ69/K70G/T215Y, and M41L/T215Y. Represented values are the fold-increase in drug susceptibility of the indicated mutant viruses compared with those obtained with recombinant HIV containing the BH10 RT sequence. Drug susceptibility values for AZT, d4T, and ritonavir are shown using black, gray, and white bars, respectively.