Rescue of transport activity in permease mutants E126D/G150A or E126D/G141A. (A) Time courses of lactose transport by E. coli T184 expressing mutant permeases E126D, E126D/G150A, E126D/G150A/A122G, or no permease (i.e., cells transformed with pT7-5 with no insert). “Unrescued mutants” refers to mutant E126D/G150A containing, in addition, mutations A120G, A124G, or A127G, which do not vary from the line shown by more than 20%. (B) Time courses of lactose transport by E. coli T184 expressing mutant permeases E126D, E126D/G141A, E126D/G141A/A127G, or no permease (i.e., cells transformed with pT7-5 with no insert). “Unrescued” refers to E126D/G141A containing mutations A120G, A122G, or A124G, which do not vary from the line shown by more than 20%.