Cell division is thought to be powered by the constriction of an actomyosin containing contractile ring found transiently in the cleavage furrow. Conventional myosin II plays a fundamental role in this process of cytokinesis where, in the form of a multimeric complex known as the bipolar thick filament, it is thought to be the molecular motor that generates the force necessary to cause ring constriction.

In order to study the dynamics of this protein in the dividing cell, we have made a fusion protein of the green fluorescent protein (GFP) and the amino terminus of the Dictyostelium myosin heavy chain (GFP-myosin), and imaged the location of this protein in dividing Dictyostelium cells were it is the only myosin II present in the cell. The addition of GFP does not compromise the functioning of the myosin motor as evidenced by the fact that purified GFP-myosin has solution ATPase and in vitro motility kinetics similar to that of non-labelled myosin. In addition, GFP-myosin fully complements the myosin null mutation for both development and cytokinesis in suspension suggesting that GFP-myosin acts as a regulated motor when expressed in cells.