BLOC-1 is a receptor for Msb3. (A and B) BLOC-1 overproduction relocalizes Msb3 to the vacuole surface. GFP-tagged Msb3, Ypt7, and Vps21 were localized by fluorescence microscopy in diploid wild-type cells or cells overexpressing the entire BLOC-1 under the control of the GAL1 promoter. Bli1-GFP was monitored only in the BLOC-1 overexpression strain. To monitor vacuole morphology, membranes were stained with FM4-64. Deconvolved images are shown. Arrowheads indicate Bli1-GFP accumulation at the vacuole–vacuole interface. Bar, 5 µm. (C) Msb3 interacts with BLOC-1. Cell lysates containing GFP-tagged Msb3 alone or with overproduced BLOC-1 complex were immunoprecipitated with IgG Sepharose. Eluates were TCA precipitated and analyzed by SDS-PAGE and Western blotting using antibodies against GFP, Vac8, and Arc1 (as a control protein). (D) BLOC-1 subunits Cnl1, Snn1, and Bli1 interact with Msb3 in vivo. VN-Msb3 and BLOC1-VC were coexpressed, and the interaction was visualized by the YFP signal. Bar, 5 µm.