FIG. 3.

(A) Accumulation of alkylated, isomerization-blocked SU-TM complexes during alkylation-inhibited fusion. XC cell-bound [³⁵S]Mo-MLV was incubated at 37°C for 0 to 60 min in fusion buffer containing 1.2 mM M135 and then washed and lysed in the absence (lanes 1 to 6) or presence (lanes 7 to 11) of 1.2 mM M135. SU-TM complexes were captured by immunoprecipitation with the complex-specific MAb 500 and analyzed by nonreducing SDS-PAGE. Note that 10 times more sample has been applied in lanes 1 to 6 than in lanes 7 to 11. The minor amounts of SU observed in most lanes are most likely generated by artificial reduction of the SU-TM disulfide bond during sample preparation for SDS-PAGE (42). (B) Quantification of alkylated, isomerization-blocked SU-TM complexes shown in panel A, lanes 1 to 6. The relative amounts of alkylated complexes at different times of incubation were calculated as percentages of the total amount of viral Env (lanes 7 to 11). (C) Correlation of the kinetics of accumulation of the alkylated, isomerization-blocked SU-TM complexes and that of fusion. The amounts of alkylated complexes at different times of incubation were calculated as percentages of that obtained in the 40-min incubation. The fusion kinetics is from Fig. 1C.