Single-Cys mutants Q241C, A244C, S311C, A312C, L313C, L329C, L330C, V331C, F334C and T338C were labeled with TMRM for 30 s at 0 °C. TMRM-labeled bands (upper panels) and silver-stained bands (lower panels) corresponding to LacY were imaged. Experiments were carried out as described in Materials and Methods and in the legend to Fig. 1.