Aip1p interacts with cofilin to disassemble actin filaments

Actin interacting protein 1 (Aip1) is a conserved component of the actin cy toskeleton first identified in a two-hybrid screen against yeast actin. Her e, we report that Aip1p also interacts with the ubiquitous actin depolymeri zing factor cofilin. A two-hybrid-based approach using cofilin and actin mu tants identified residues necessary for the interaction of actin, cofilin, and Aip1p in an apparent ternary complex. Deletion of the AIP1 gene is leth al in combination with cofilin mutants or act1-159. an actin mutation that slows the rate of actin filament disassembly in vivo. Aip1p localizes to co rtical actin patches in yeast cells, and this localization is disrupted by specific actin and cofilin mutations Further, Aip1p is required to restrict cofilin localization to cortical patches. Finally, biochemical analyses sh ow that Aip1p causes net depolymerization of actin filaments only in the pr esence of cofilin and that cofilin enhances binding of Aip1p to actin filam ents. We conclude that Aip1p is a cofilin-associated protein that enhances the filament disassembly activity of cofilin and restricts cofilin localiza tion to cortical actin patches.