De novo formation of actin filaments from the side of mother filaments plays crucial roles at the leading edge of motile cells and in endocytosis. The seven-subunit Arp2/3 complex initiates these actin filament branches. Fission yeast S. pombe has been used as a genetic model organism on studying the mechanism of endocytosis and cytokinesis. However, there is a gap between microscopic observations in pombe cells and in vitro biochemistry because most of the biochemical and biophyscical properties of the fission yeast actin binding proteins have been done with muscle skeletal actin for matters...