Panels A and B, growth competition assays of virus with the D10 RT in which K101E (panel A) or [M41L+T215Y] (panel B) were reverted to wild-type, competed against NL4-3 with the intact D10 RT as a reference strain. The average and standard deviation of the production rate ratio (PRR) is shown on each graph. Panel C, EFV susceptibility assays with variants of D10 in which different resistance mutations were reverted to wild-type. The peak EFV-dependent stimulation concentration for D10 with M41L+T215Y back mutated to wild-type was 3200 nM EFV and the fold stimulation was 100.73±28.8. EFV, EFV; wt, wild-type.