Myosin-II tails confer unique functions in Schizosaccharomyces pombe:: Characterization of a novel myosin-II tail

Schizosaccharomyces pombe has two myosin-IIs, Myo2p and Myp2p, which both concentrate in the cleavage furrow during cytokinesis. We studied the phenotype of mutant myosin-II strains to examine whether these myosins have overlapping functions in the cell. myo(2+) is essential. myp(2+) cannot rescue loss of myo(2+) even at elevated levels of expression. myp(2+) is required under specific nutritional conditions; thus myo(2+) cannot rescue under these conditions. Studies with chimeras show that the tails rather than the structurally similar heads determine the gene-specific functions of myp(2+) and myo(2+). The Myo2p tail is a rod-shaped coiled-coil dimer that aggregates in low salt like other myosin-II tails. The Myp2p tail is monomeric in high salt and is insoluble in low salt. Biophysical properties of the full-length Myp2p tail and smaller subdomains indicate that two predicted coiled-coil regions fold back on themselves to form a rod-shaped antiparallel coiled coil. This suggests that Myp2p is the first type II myosin with only one head. The C-terminal two-thirds of Myp2p tail are essential for function in vivo and may interact with components of the salt response pathway.