Movement of myosin-coated fluorescent beads on actin cables in vitro.

Myosin-coated fluorescent beads are observed to move unidirectionally along organized actin filament arrays in the alga, Nitella, with an average velocity similar to in vivo rates of movement in muscle and other cells. The myosin produces the motive force, as the movement is ATP dependent and is blocked by inactivation of the myosin heads. The movement, which occurs in the absence of bipolar thick filaments, provides a quantitative assay for myosin motility.