The general research interest of Dr. Spudich's laboratory is the molecular basis of cell motility. They have three specific research interests, the molecular basis of energy transduction that leads to ATP-driven myosin movement on actin, the biochemical basis of the regulation of actin and myosin interaction and their assembly states, and the roles these proteins play in vivo, in cell movement and changes in cell shape.
They work on two experimental systems: contraction of mammalian muscle and chemotaxis of Dictyostelium discoideum cells. Each of these systems has its special advantages. Skeletal muscle has the most highly organized contractile apparatus of any cell type, and the chemistry and biochemistry of muscle actin and myosin are most advanced.
Dictyostelium discoideum, the cell that commands most of our attention, exhibits all of the behavior of nonmuscle mammalian cells and, unlike other eukaryotic cells, can be grown in large amounts for biochemical work. Furthermore, DNA-mediated transformation is being applied to this organism, and they have demonstrated efficient gene targeting by homologous recombination in the myosin gene, which they have cloned and sequenced.
Their approaches include biochemical and structural studies of actin, myosin, and associated regulatory proteins. In addition, they have designed and developed in vitro assays for ATP-dependent movement of purified myosin on filaments reconstituted from purified actin. These assays allow them to analyze mutant myosin molecules for altered function. The site-directed mutagenized forms of myosin are obtained by gene cloning and expression in an appropriate host. Their demonstration that the Dictyostelium discoideum myosin gene can undergo homologous recombination allows us to also probe the effects of the altered myosin forms on the phenotype of the cell.