ABSTRACT
This chapter describes the structure and motile properties of myosin II, which drives muscle contraction, as well as numerous contractile processes in nonmuscle cells. It examines the families of 'unconventional' myosins, which come in a rich variety of shapes and sizes and have often unexpected functions. The chapter highlights the importance of recombinant DNA studies and genetics in analysis of the cytoskeleton. It examines that myosin II molecules assemble into bipolar filaments that can cause actin filaments to contract if supplied with ATP. The chapter discusses that mutants of Dictyostelium lacking the gene for myosin II can perform cytokinesis, although their efficiency is impaired. It seems that in its most generic form, animal cell division is driven by a flow of actin from the opposing poles toward center of the cell, driven by regional differences in actin assembly and disruption. Both Acanthamoeba and Dictyostelium have multiple myosin I genes, which gene knockout studies suggest act in concert or have overlapping functions.
