Phosphatidylinositol-dependent actin filament binding by the SWI/SNF-like BAF chromatin remodeling complex

Recently, several chromatin remodeling complexes in yeast, Drosophila, and mammals have been shown to contain actin and actin-related proteins (arps). However, the function of actin in these complexes is unclear. Here, we show that the mammalian SWI/SNF-like BAF complex binds to phosphatidylinositol 4,5-bisphosphate (PIP(2)) micelles and PIP(2)-containing mixed lipid vesicles, and that PIP(2) binding allows the complex to associate with actin pointed ends and branch points. Actin binds to at least two distinct domains in the C terminus of the Brg1 protein, and interaction with only one of these domains is sensitive to PIP(2). Based on these findings, we propose a model for PIP(2) activation of actin binding by relief of intramolecular capping of actin by Brg1.