Functional reconstitution of ypt7p GTPase and a purified vacuole SNARE complex.

Membrane trafficking has heretofore been studied with intact organelles. Here, fusion-competent proteoliposomes were reconstituted from a yeast vacuole detergent extract. Homotypic vacuole fusion requires many membrane proteins, including the Ypt7p guanosine triphosphatase and a "SNARE complex" with Vam3p and Nyv1p. Proteoliposomes from extracts immunodepleted of either Vam3p or Ypt7p could not fuse, but vesicles reconstituted from a mixture of these depleted extracts had restored fusion activity. Purified preassembled vacuolar SNARE complex, when reconstituted with a SNARE-depleted extract, was fully functional for fusion. Thus, solubilized integral membrane components can be reconstituted for priming, docking, and fusion steps of organelle trafficking.