The long term aim of the research is to understand atomic resolution the signal transduction pathways that regulate the cells cytoskeleton. Cytoskeletal features play critical roles in cell development, maintenance and in some cases in cell motility (e.g. in invasive cancer cells). I will characterize components of a signaling pathway that originates from receptors in the plasma membrane, involves small GTPases and utilizes proteins belonging to the WASP family. Specifically the NMR solution structure of human p21-Arc, a protein belonging to the Arp2/3 complex, will be determined. Interactions of p2l-Arc with effectors such as WASP will be studied by high resolution spectroscopic and biochemical approaches. The Arp2/3 complex appears to be ubiquitous to eukaryotic cells and nucleates the polymerization of actin. The proposed research will help to understand how actin polymerization is initiated and controlled in cells.