Binding of Sly1 to Sed5 enhances formation of the yeast early Golgi SNARE complex

SLY1 is an essential gene for vesicular transport between the ER and the early Golgi apparatus in Saccharomyces cerevisiae. It encodes a hydrophilic Sec1/Munc18 family protein that binds to the t-SNAREs. The amount of Sly1 protein that coprecipitated with the t-SNARE Sed5 was much reduced in a temperature-sensitive sly1(ts) mutant yeast compared with the wildtype. The mutant Sly1(ts) protein was shown to have a reduced binding activity to Sed5. In the wildtype, a detectable amount of Sly1 was found in the complex between Sed5 and the v-SNARE Bet1. In vitro formation of this complex on different membranes in yeast lysate was enhanced by the addition of recombinant Sly1. These results indicate that binding of Sly1 to Sed5 enhances trans-SNARE complex formation.