Correlation between cross-linking and transport activity of P28C/C154 in RSO membrane vesicles. A, Western blots of RSO vesicles containing the P28C/C154 mutant with tandem fXa sites. B, active transport. Cross-linking, fXa digestion, and [1-14C]lactose transport assays were performed as described in the legend to Fig. 3. ■, control; ●, treated with 0.5 mm Cu/Ph; ▴, treated with 10 mm TDG and 0.5 mm Cu/Ph; ▾, treated with 0.05 mm (MTS)2-1; ♦, treated with 10 mm TDG and 0.05 mm (MTS)2-1; ◀, vector pT7-5. C, native Cys154 and a Cys replacement for Pro28 are denoted by sticks based on the structure of LacY (PDB code 2V8N).