PITPβ promotes COPI vesicle fission through lipid transfer and membrane contact formation.

Intracellular transport among organellar compartments occurs in two general ways: by membrane-bound carriers and membrane contacts. Specific circumstances that involve the coordination of these two modes of transport remain to be defined. By studying coat protein I (COPI) transport, we find that phosphatidylcholine with short acyl chains (sPC) is delivered through membrane contact from the endoplasmic reticulum (ER) to sites of COPI vesicle formation at the Golgi to support the fission stage. Phosphatidylinositol transfer protein beta (PITPβ) plays a key role in this process, with the elucidation of this role shedding new insights into how PITPβ acts, providing a mechanistic understanding of a specific circumstance when vesicular transport requires membrane contact and contributing to the general understanding of how intracellular transport carriers are formed.