COPII under the microscope.

Transport through the secretory pathway begins with COPII regulation of ER export. Driven by the Sar1 GTPase cycle, cytosolic COPII proteins exchange on and off the membrane at specific sites on the ER to regulate cargo exit. Here recent developments in COPII research are discussed, particularly the use of live-cell imaging, which has revealed surprising insights into the coat's role. The seemingly static ER exit sites are in fact highly dynamic, and the ability to visualise trafficking processes in intact living cells has highlighted the adaptable nature of COPII in cargo transport and the emerging roles of auxiliary factors.