YPT1P IMPLICATED IN V-SNARE ACTIVATION

SYNAPTOBREVIN-LIKE membrane proteins that reside on transport vesicles , called the vesicle SNARE (v-SNARE), play a key role in ensuring that a vesicle targets and fuses with its correct acceptor compartment(1-3 ). Here we show that Bos1p, the v-SNARE of yeast endoplasmic reticulum -to-Golgi transport vesicles, pairs with another integral membrane pro tein of similar topology (Sec22p) on vesicles. This pairing, which app ears to require functional Ypt1p (Rab in mammalian cells), may aid the activity of Bos1p on this compartment. These findings suggest that Ra bs regulate the specificity of membrane fusion by selectively activati ng the v-SNARE on carrier vesicles. Because the v-SNARE resides on mor e than one membrane, such a regulated activation step may be necessary to prevent the premature fusion of donor and acceptor compartments(4) .