Members of the Munc 18/Sec1 family, such as Sly 1p, play essential roles in membrane trafficking. The proteins bind to t-SNAREs (components of the SNARE complexes that drive membrane fusion); however, their exact role is far from clear, since some experiments suggest that they can inhibit membrane fusion. Koji Yoda and co-workers now demonstrate that Sly 1p directly stimulates SNARE assembly (see p. 3683). They show that the interaction between Sly 1p and the t-SNARE Sed5p is significantly reduced in a temperature-sensitive Sly1tsmutant and that Sly1pts protein has a lower affinity for Sed5p than does its wild-type counterpart. Most significant, however, is the authors' use of a novel in vitro assay for SNARE complex assembly in Sly1ts mutant lysates, in which they show that purified Sly1 protein stimulates the formation of trans-SNARE complexes involving Sed5p and its partner the v-SNARE Bet1p. Since Sly1p-Sed5p binding is unaffected by SNARE complex formation, Yoda and co-workers propose that Sly1p acts prior to complex formation; the Munc 18/Sec1 family might thus function by binding to t-SNAREs and inducing a `pro-v-SNARE' binding state.

© The Company of Biologists Limited 2002
2002