Figure 4.

The SNARE chaperones Sec17p and Sec18p are involved in ATP/GTP-driven ER fusion. (A) Sec17p and Sec18p are involved in ATP/GTP-driven ER fusion, but not in GTP-driven fusion. Gluc1 and Gluc2 microsomes were incubated on ice or at 27°C in the presence of GTP or ATP/GTP for 90 min. Some reactions were treated with anti-Sec17p antibodies, anti-Sec18p antibodies, or recombinant his₆-Sec18p at the indicated concentrations. Data represent the means ± SEM (error bars; n = 3). **, P < 0.01; ***, P < 0.001, between GTP-only-driven reactions; #, P < 0.05; ###, P < 0.001, between ATP/GTP-driven reactions, Tukey’s test compared with the “no inhibitor” group. (B) In vitro yeast vacuole fusion reactions were efficiently prevented by anti-Sec17p or anti-Sec18p antibodies. Data represent the means ± SEM (error bars; n = 3). Lowercase letters indicate statistically different groups (P < 0.001, Tukey’s test). (C) Recombinant his₆-Sec18p can rescue the fusion of anti-Sec18p–treated vacuoles. BJ3505 and DKY6281 vacuoles were incubated in the presence of anti-Sec18p antibodies at 27°C. After 20 min, recombinant his₆-Sec18p was added at the indicated concentrations, and the mixture was further incubated for 70 min at 27°C. Data represent the means ± SEM (error bars; n = 3). Lowercase letters indicate statistically different groups (P < 0.01, Tukey’s test).