Arf1 Directly Recruits the Pik1‐Frq1 PI4K Complex to Regulate the Final Stages of Golgi Maturation

Abstract

Proper Golgi complex function depends on the activity of Arf1, a GTPase whose effectors assemble and transport outgoing vesicles. Phosphatidylinositol 4-phosphate (PtdIns4P) generated at the Golgi by the conserved PI 4-kinase Pik1 (PI4KIIIβ) is also essential for Golgi function, although its precise roles in vesicle formation are less clear. Arf1 has been reported to regulate PtdIns4P production, but whether Pik1 is a direct Arf1 effector has not been established. Using a combination of live-cell time-lapse imaging analyses, acute PtdIns4P depletion experiments, and in vitro protein-protein interaction assays on Golgi-mimetic membranes, we have found that Arf1 initiates the final stages of Golgi maturation by tightly controlling PtdIns4P production through direct recruitment of the Pik1-Frq1 PI4-kinase complex. This PtdIns4P serves as a critical signal for AP-1 and secretory vesicle formation, the final events at maturing Golgi compartments. This work, along with ongoing structural investigations, establishes the regulatory and temporal context surrounding Golgi PtdIns4P production and its precise roles in Golgi maturation.