9405738 Fechheimer Cell movements such as phagocytosis, chemotaxis, and cytokinesis require precise control of the assembl of actin filaments into either randomly gelled networks or highly polarized bundles. Formation of these cross-linked actin structures is mediated by actin cross-linking proteins. This project focuses on the structure and function of the Dictyostelium 30,000 dalton actin bundling protein, one of eight actin cross-linking proteins present in Dictyostelium. The binding sites for actin and calcium ion, and the parameters controlling the formation of either actin gels or bundles will be investigated. The molecular mechanisms by which the 30 kD protein is recruited to the phagocytic cup during ingestion of food, the cleavage furrow during cytokinesis, and sites of cell to cell contact in developing cells will be investigated. The function of the 30 kD protein in cell structure and movement in Dictyostelium will be probed using gene disruption by homologous recombination to create cells lacking the 30 kD actin bundling protein. This work will promote our understanding of molecular mechanisms of cell movements essential to the growth and division of eucaryotic cells. Significance also derives from probing the apparent redundancy of function of actin cross-linkng proteins. %%% Cell movements, such as phagocytosis, locomotion, cytokinesis, morphogenetic transformations accompanying cellular differentiation are essential to the life of eucaryotic organisms. Actin microfilaments contribute to the control of cell shape and generation of mechanical force for cell movements. The properties of actin in cells must be explained from the structure and chemistry of actin and the properties of actin binding proteins. The conservation of actin binding proteins throughout the eucaryotes provides strong evidence for the significance of these proteins as regulators of actin utilization by cells. Studies of the structures and functions of these protein s will provide important insights into the control of cell shape and motility in eucaryotes. In addition, understanding of the molecular basis for actin microfilament assembly and organized supra-assembly is a critical prerequisite to the exploitation of cellular structures and biomolecular machines by materials scientists and nanofabrication engineers. ***
