Myosin-II Tails Confer Unique Functions inSchizosaccharomyces pombe: Characterization of a Novel Myosin-II Tail

Abstract

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.myo2 + is essential.myp2 + cannot rescue loss ofmyo2 + even at elevated levels of expression.myp2 + is required under specific nutritional conditions; thus myo2 + cannot rescue under these conditions. Studies with chimeras show that the tails rather than the structurally similar heads determine the gene-specific functions ofmyp2 + and myo2 +. 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.

Molecular organization of cytokinesis nodes and contractile rings by super-resolution fluorescence microscopy of live fission yeast

“…The two N-terminal motor heads bind light chains and actin filaments. The remainder of each heavy chain forms a coiled-coil tail ∼65 nm long with a 20-nm tail piece (39). The C-terminal ends of the Myo2p tails concentrated near the plasma membrane within a radius of 33 nm, a distribution indistinguishable from mEos3.2-Rng2p by KS testing (Fig.…”

An actin–myosin-II interaction is involved in maintaining the contractile ring in fission yeast

“…Given that myo3-S469V cells did not exhibit a morphological phenotype in 1 M KCl, maintenance of the contractile ring might be the primary role of Myo3, which could be separate from its role in tolerance of high concentrations of the Cl − ion. Assuming that a signaling cascade is activated under high-Cl − ion conditions, it is possible that Myo3 provides a scaffold for signal transduction in which signaling molecules interact, as has already been speculated (Bezanilla and Pollard, 2000).…”

“…A previous study has demonstrated that the recombinant Myo3 tail is monomeric because it formed an intramolecular coiled-coil and, hence, Myo3 is a single-headed myosin-II (Bezanilla and Pollard, 2000). However, contractile-ring-localized Myo3 might be in large assemblies because most of the Myo3 signal appeared as dozens of motile puncta.…”

“…After being joined to the ring at late anaphase, Myo3 might collaborate with Myo2 in its maintenance and constriction. Based on the functional equivalency of the motor heads between Myo3 and Myo2 (Bezanilla and Pollard, 2000), the two myosin-II proteins might work in parallel using a similar mechanism. Given that half of the myo2-E1 myo3-S469V cells displayed constriction of the contractile ring, whereas the other half did not, a minimum requirement (i.e.…”

“…A double mutation of myo3Δ (a null mutation in myo3) and the myo2-E1 (a temperature-sensitive allele of myo2; Balasubramanian et al, 1998) have previously been shown to cause severe defects in cytokinesis (Motegi et al, 2000). The motor heads of Myo2 and Myo3 are assumed to have similar properties because they have been found to be functionally exchangeable (Bezanilla and Pollard, 2000). Thus, although the two myosin-II proteins have been suggested to play an overlapping role, possibly through their head moieties, the underlying mechanism currently remains unclear.…”