Distinct biochemical requirements for the budding, targeting, and fusion of ER-derived transport vesicles.

TLDR

Transport of pro‑alpha‑factor from the ER to the Golgi in yeast spheroplasts occurs via diffusible vesicles that contain core‑glycosylated pro‑alpha‑factor and require ATP, Sec12p, Sec23p, and GTP hydrolysis for formation. The vesicles transfer pro‑alpha‑factor to the Golgi more rapidly and efficiently than the ER, do not need Sec12p or Sec23p for transfer, are resistant to GTPγS, and their targeting and fusion depend on Ypt1p, Sec18p, calcium, and ATP.

Abstract

The transport of pro-alpha-factor from the ER to the Golgi apparatus in gently lysed yeast spheroplasts is mediated by diffusible vesicles. These transport vesicles contain core-glycosylated pro-alpha-factor and are physically separable from donor ER and target Golgi compartments. The formation of diffusible vesicles from the ER requires ATP, Sec12p, Sec23p, and GTP hydrolysis. The vesicles produced are functionally distinct from the ER: they transfer pro-alpha-factor to the Golgi apparatus faster and more efficiently than the ER, they do not require Sec12p or Sec23p to complete transfer, and transfer is resistant to GTP gamma S. Targeting of vesicles to the Golgi apparatus requires Ypt1p and Sec18p. Fusion of vesicles that have targeted requires calcium and ATP.