CR16 forms a complex with N-WASP in brain and is a novel member of a conserved proline-rich actin-binding protein family

The Neuronal Wiskott-Aldrich syndrome protein (N-WASP) has emerged as a cen tral regulator of the actin cytoskeleton with abilities to integrate multip le upstream signal inputs and transmit them to the Arp2/3 complex. Here, we demonstrate that native N-WASP is present in a tight complex with a prolin e-rich protein, CR16, which shares approximate to 25% identity with WASP in teracting protein. CR16 is encoded by a gene previously cloned as a glucoco rticoid-regulated mRNA from a rat hippocampal cDNA library. Although N-WASP is expressed ubiquitously, full-length CR16 protein is found predominately in the brain. CR16 and N-WASP colocalize in primary hippocampal neurons an d at the tips of their growth cone filopodia. In vitro, CR16 directly binds both monomeric and filamentous actin but does not affect the kinetics of a ctin polymerization mediated by N-WASP and the Arp2/3 complex. Sequence hom ologues of CR16 are found not only in other vertebrates but also in the inv ertebrate Caenorhabditis elegans and in yeast. Thus, CR16 and WASP interact ing protein belong to a family of N-WASP-binding proteins.