title: A soluble motor from the alga Nitella supports fast movement of actin filaments in vitro.
abstract: In the streaming cytoplasm of the Characean algae cell, the movement of organelles along actin bundles occurs at a striking rate of up to 60 microns s-1. To further characterize the molecular mechanisms responsible for this phenomenon, we have reconstituted the movement of actin filaments in vitro using defined biochemical components. We report that only a soluble cytoplasmic fraction devoid of organelles and filamentous material supports the movement of fluorescent-labeled actin filaments on glass at a rate of up to 60 microns s-1. This fraction also contains the K(+)-EDTA ATPase and the actin-activated Mg2+ ATPase activities characteristic of myosin proteins. Therefore, on the basis of these observations, we conclude that Nitella cells have a soluble pool of non-filamentous myosin molecules with the mechanochemical properties expected for a motor responsible for cytoplasmic streaming in vivo. The preparation and conditions described here should be useful for the purification of this translocator.
mesh_terms: D000199:Actins / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D003599:Cytoskeleton / Q000648:ultrastructure; D056890:Eukaryota / Q000378:metabolism*; D018715:Microscopy, Video; D009218:Myosins / Q000378:metabolism*; D011817:Rabbits
chemical_list: D000199:Actins; D009218:Myosins