The structural and functional significance of the actin microfilament system in nonmuscle cells in cell motility and growth will be analyzed. Using biochemistry, cell biology, immunology, and molecular biology, an integrated approach to this problem will be followed. Through the production of highly specific monoclonal antibodies directed against three Ca2+ regulated microfilament components (alpha-actinin, vinculin and myosin light chain kinase) and the subsequent microinjection of these antibodies into living nonmuscle cells, the functional roles of these proteins will be determined. Through the microinjection of Ca2+/EGTA buffers into living cells, the role of Ca2+ in the dynamics of the microfilament system will be studied. And, through the molecular cloning of the genes encoding the biochemically distinct muscle and nonmuscle forms of both alpha-actinin and vinculin, the molecular basis for the different biochemical activities will be examined.