Intracellular transport is now appreciated to occur through two general types of carriers, either vesicles , or tubules , . Coat proteins act as the core machinery that initiates vesicle formation , , but the counterpart that initiates tubule formation has been unclear. Here, we find that the Coat Protein I (COPI) complex initially drives the formation of Golgi buds. Subsequently, a set of opposing lipid enzymatic activities determines whether these buds become vesicles or tubules. Lysophosphatidic acid (LPA) acyltransferase type γ (LPAAT–γ) promotes COPI vesicle fission for retrograde vesicular transport. In contrast, cytosolic phospholipase A2 type α (cPLA2–α) inhibits this fission event to induce COPI tubules, which act in anterograde intra-Golgi transport and Golgi ribbon formation. These findings not only advance a molecular understanding of how COPI vesicle fission is achieved, but also shed new insight into how COPI acts in intra-Golgi transport and reveal an unexpected mechanistic relationship between vesicular and tubular transport.
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