YOR068p promotes vacuole fusion. (A) Fusion reactions with vacuoles from BJ3505 and DKY6281 were performed with anti-Vam3p antibody (1 μM), calmodulin (CaM; 20 μM), his6-Sec18p (0.1 μM), or MBP-tagged Vam10p (Vam10p; 8 μM) as indicated. (B) Fusion reactions contained the indicated concentrations of MBP, Yor068p, or Ydr136p, each with an MBP tag. (C) Fusion reactions bore control buffer (lanes 1 and 2) or the indicated concentrations of anti-Vam10p (lanes 3 and 4) or anti-Ydr433p antibody. These IgG antibodies were purified as described (18). (D) Standard fusion reactions contained PS buffer (10 mm Pipes-KOH, pH 6.8/200 mm sorbitol; lanes 1 and 2) or the indicated concentrations of anti-Vam10p antibody (IgG fraction; lanes 3 and 5–7) and/or Vam10p (lanes 4–7).