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The Golgi Arf‐GEFs Gea1 and Gea2 are regulated by their HDS3 domains and the Rab GTPase Ypt1 (LB157)

The Golgi Arf GTPases control the sorting of membranes and proteins through all eukaryotic cells, recruiting adapters and cargo to sites of vesicle formation when in their activated GTP‐bound form. Arf guanine nucleotide exchange factors (Arf‐GEFs) are the master regulators of Arf activation and are conserved throughout eukaryotes. Two Arf‐GEFs, Gea1 and Gea2, function at the cis‐Golgi in Saccharomyces cerevisiae, but we know relatively little about how these GEFs are regulated. Recent work with their close relative at the trans‐Golgi network, Sec7, has revealed that recruitment of Sec7 to the trans‐Golgi network and relief of its autoinhibition are dependent on its C‐terminal domains, as well as on positive feedback from Arf1 and other protein interactions. The Golgi Arf‐GEFs share predicted domain architecture, suggesting that Gea1/2 may be regulated by mechanisms similar to those of Sec7. However, the specific proteins which orchestrate the activation and localization of Sec7 do not appear to act upon Gea1/2. In vitro biochemical studies, genetics, and live cell microscopy have revealed two contributing factors in Gea1/2 regulation: an interaction with the Rab GTPase Ypt1 and the regulatory roles of one of the domains of Gea1/2. Combined with structural studies, these results will define general features of Golgi Arf‐GEF regulation and localization, as well as features specific to Gea1 and Gea2, providing fundamental insight into how Arf1 is regulated at the Golgi.