We are interested in the structure, regulation and in vivo functions of small myosins in nonmuscle cells. Our approach is to use anatomical, biochemical, cell biological and molecular genetic methods to study myosin I, a low-molecular weight, monomeric, nonfilamentous form of nonmuscle myosin. Current efforts are directed at: (1) determining the in vivo functions of myosin I by examining the phenotype of myosin I-deficient cells generated by molecular genetic means, (2) structure/function analyses of the unconventional C-terminal domains of myosins I (both protozoan myosin I and a vertebrate form of myosin I, the intestinal brush border 110 kDa protein), and (3) full characterization of an apparent high - molecular-weight form of protozoan myosin I. These basic studies shed light on the molecular basis of actomyosin-linked cellular motility, which in turn may increase our understanding of many cellular processes crucial to clinical medicine, such as white blood cell chemotaxis, cancer cell migration, angiogenesis, and wound healing.