Project Summary/Abstract My laboratory pursues answers to fundamental questions in cell biology. Broadly, we study how self-assembly of complex macromolecular structures —especially cytoskeletal polymers and networks— creates spatial order in living cells. To understand how molecular properties govern the architecture and function of living cells, we perform quantitative studies at multiple size scales: (i) single-molecule and bulk biochemical studies of cytoskeletal components; (ii) biophysical and microscopical studies of complex cellular structures reconstituted in vitro; and (iii) cell biological and high-resolution microscopy studies of cytoskeletal systems in living cells. Our work currently addresses the following topics: (1) function and regulation of actin network motors that make use of the Arp2/3 complex; (2) pseudopod assembly and amoeboid locomotion; (3) autophagy and endomembrane movement; (4) nuclear actin assembly and DNA repair; and (5) assembly and function of cytoskeletal elements in eubacteria and archaea. As part of an international consortium we have also recently begun work to understand how SARS-CoV2 induces formation of long, branched filopodia in infected host cells and what function these filopodia play in viral egress and spread.