THE FASTEST ACTIN-BASED MOTOR PROTEIN FROM THE GREEN-ALGAE, CHARA, AND ITS DISTINCT MODE OF INTERACTION WITH ACTIN

The endoplasmic streaming in Characean cells is an actin-dependent mov ement, The motor protein responsible for the streaming was partially p urified and characterized, It was soluble at low ionic strength, an AT Pase of a molecular mass of 225 kDa and activated more than 100 times by muscle F-actin, Surprisingly, in an in vitro motility assay, the mo tor protein moved muscle F-actin at 60 mu m/s, which is similar to the velocity of streaming in a living cell and 10 times faster than muscl e myosin, Proteolytic cleavage of actin impaired movement crucially on muscle myosin, but did not affect movement at all on the Chara motor protein, suggesting that the Chara motor protein would interact with a ctin via a set of sites different from those of muscle myosin.