Nucleation of COPII vesicular coat complex by endoplasmic reticulum to Golgi vesicle SNAREs.

Protein trafficking from the endoplasmic reticulum (ER) to the Golgi apparatus involves specific uptake into coat protein complex II (COPII)-coated vesicles of secretory and of vesicle targeting (v-SNARE) proteins. Here, two ER to Golgi v-SNAREs, Bet1p and Bos1p, were shown to interact specifically with Sar1p, Sec23p, and Sec24p, components of the COPII coat, in a guanine nucleotide-dependent fashion. Other v-SNAREs, Sec22p and Ykt6p, might interact more weakly with the COPII coat or interact indirectly by binding to Bet1p or Bos1p. The data suggest that transmembrane proteins can be taken up into COPII vesicles by direct interactions with the coat proteins and may play a structural role in the assembly of the COPII coat complex.