Cloning and characterization of a myosin from characean alga, the fastest motor protein in the world.

In characean algae, very rapid cytoplasmic streaming is generated by sliding movement of an unconventional myosin on fixed actin cables. The speed of this sliding movement is the fastest among many molecular motors known so far. We have cloned a set of overlapping cDNAs encoding the heavy chain of this myosin by immunoscreening with antibody raised against characean myosin. The molecular mass of this heavy chain is 248 kDa, and the protein has a conserved motor domain, six IQ motifs, an extensive alpha-helical coiled-coil domain, and a C-terminal globular domain. Phylogenetic analysis suggested that this myosin belongs to class XI.