HOPS complex activity assay. Vps11-1ts (CSY9 and CSY10) and VPS11 (BY4742 pep4Δ∷kanMX6 and BY4742 pho8Δ∷kanMX6) vacuoles were assayed for fusion in the presence of pure HOPS complex and rVam7p. HOPS buffer was added, so the total volume of pure HOPS and HOPS buffer was 9 μl. Filled arrows indicate the fusion signal observed with the concentrations of pure HOPS complex (2.2 nM) and rVam7p was (3.7 nM) used in the fusion assays in the remainder of this paper. Means and standard deviations for fusion signals observed in three independent experiments are shown. (A) Pure HOPS added to vps11-1ts vacuoles, with the indicated concentrations of rVam7p. (B) Pure HOPS added to VPS11 vacuoles, with the indicated concentrations of rVam7p. (C) rVam7p added to vps11-1ts vacuoles, with or without pure HOPS. (D) rVam7p added to VPS11 vacuoles, with or without pure HOPS.