Figure 1.

Rab1b participation in sequential transport stages at the ERES: (A) Formation and budding of COPII vesicles; Rab1b depletion induces COPII vesicle accumulation. (B) Homotypic fusion of COPII vesicles and formation of VTCs: Rab1b co-localizes with these structures. (C and D) Maturation of VTCs: Rab1b recruits GBF1, which induces COPI recruitment required for the forward movement of VTCs to the cis-Golgi. BFA treatment inhibits GBF1 membrane association without disturbing Rab1b recruitment. More details are provided in the text.