ABSTRACT
Movement of cells or their components is a fundamental activity of eukaryotic cells. The segregation of chromosomes, transport of organelles, and movement of ciliated cells are all possible owing to the large repertoire of molecular motors. Three superfamilies of motor proteins exist-myosins, kinesins, and dyneins-all of which convert chemical energy into mechanical work. Myosins are further defined by their ability to bind actin, to hydrolyze adenosine triphosphate (ATP), and to translocate along actin filaments. The function of this group of molecular motors includes many crucial cellular activities such as membrane trafficking, cell locomotion, signal transduction, and vesicle transport (reviewed in Refs. 1, 2). Myosins have historically been divided into two groups: the conventional myosins (myosin II), which include the two-headed, filament-forming dimeric myosins of skeletal muscle, smooth muscle cells; and nonmuscle cells; and the unconventional myosins (myosin I, III-XVIII).
