YEAST SYNAPTOBREVIN HOMOLOGS ARE MODIFIED POSTTRANSLATIONALLY BY THE ADDITION OF PALMITATE

Yeast possess two homologs of the synaptobrevin family of vesicle-asso ciated membrane proteins that function in membrane recognition and ves icle fusion. Yeast proteins Snc1 and Snc2 localize to secretory vesicl es and are required for constitutive exocytosis. They also form a phys ical complex with a plasma membrane protein, Sec9, which is necessary for vesicle docking and fusion to occur in vivo. Formation of this mol ecular complex, as a prerequisite for vesicle fusion, appears to have been conserved evolutionarily. Here we demonstrate that Snc proteins u ndergo a single posttranslational modification with the addition of a palmitate moiety to Cys-95 in Snc1. Modification of Cys-95 (which is l ocated proximal to the transmembrane domain) is rapid, occurs in the e ndoplasmic reticulum, and is long-lasting. Mutation of Cys-95 to Ser-9 5 blocks palmitoylation and appears to affect Snc protein stability. T his provides evidence that synaptobrevin like proteins are modified po sttranslationally, and we predict that fatty acylation may be common t o those found in higher eukaryotes.