Type II myosin involved in cytokinesis in the fission yeast,Schizosaccharomyces pombe

Abstract

We have cloned an unique gene encoding the heavy chain of a type II myosin in the fission yeast, Schizosaccharomyces pombe. The myo2+ gene encodes a protein of 1526 amino acids with a predicted molecular weight of 177 kDa and containing consensus binding motifs for both essential and regulatory light chains. The S. pombe myo2+ head domain is 45% identical to myosin IIs from Saccharomyces cerevisiae and Homo sapiens and 40% identical to Drosophila melanogaster. Structurally, myo2+ most closely resembles budding yeast MYO1, the tails of both myosin IIs containing a number of proline residues that are predicted to substantially disrupt the ability of these myosins to form coiled coils. The myo2+ gene is located on chromosome III, 8.3 map units from ade6+. Deletion of approximately 70% of the coding sequence of myo2+ is lethal but myo2Δ spores can acquire a suppressor mutation that allows them to form viable microcolonies consisting of filaments of branched cells with aberrant septa. Overexpression of myo2+ results in the inhibition of cytokinesis; cells become elongated and multinucleate and fail to assemble a functional cytokinetic actin ring and are either aseptate or form aberrant septa. These results suggest that a contractile actin‐myosin based cytokinetic mechanism appeared early in the evolution of eukaryotic cells and further emphasise the utility of fission yeast as a model organism in which to study the molecular and cellular basis of cytokinesis. Cell Motil. Cytoskeleton 38:385–396, 1997. © 1997 Wiley‐Liss, Inc.

Localization of Fission Yeast Type II Myosin, Myo2, to the Cytokinetic Actin Ring Is Regulated by Phosphorylation of a C-Terminal Coiled-Coil Domain and Requires a Functional Septation Initiation Network

“…A similar phenotype is seen when Cdc7 and Spg1 are overexproduced (Fankhauser and Simanis, 1994;Schmidt et al, 1997). The evidence that the SIN pathway also regulates Myo2 function includes a strong genetic interaction between a myo2 deletion strain and cdc7-24 (May et al, 1997) and the reduced efficiency of septation in myo2 mutants after overexpression of Spg1 or Cdc7, or the inactivation of Cdc16 (Mulvihill et al, 2000). This raises the question as to whether the Myo2 heavy chain is a substrate for Cdc7 or a downstream kinase, or whether regulation could work through an associated light chain.…”

“…The amino terminal half (the first 2302 base pairs) of the myo2 ϩ gene was isolated from the plasmid pBluemyo2 ϩ (May et al, 1997) as an SalI-BamHI fragment and was ligated into SalI-BamHI cut pREP41Negfp ϩ (Craven et al 1998) to give the plasmid pREFP41gfp-myo2 768 . The carboxyl-terminal half (the last 2275 base pairs) of the myo2 ϩ gene was isolated from pBluemyo2 ϩ as a BamHI-BamHI fragment and was ligated into the BamHI site of pREP41gfp-myo2 768, to give pREP41gfp-myo2 ϩ .…”

“…Fission yeast cells divide by means of a contractile actin ring (CAR) that both positions the cytokinetic septum and determines its structural and functional integrity (Marks and Hyams, 1985). The CAR contains two type II myosins encoded by the genes myo2ϩ May et al, 1997) and myp2ϩ/myo3ϩ (Bezanilla et al, 1997;Motegi et al, 1997). Myo2 is an essential component of the CAR May et al, 1997).…”

“…The CAR contains two type II myosins encoded by the genes myo2ϩ May et al, 1997) and myp2ϩ/myo3ϩ (Bezanilla et al, 1997;Motegi et al, 1997). Myo2 is an essential component of the CAR May et al, 1997). Cytokinesis can proceed in the absence of Myp2 but less efficiently than when it is present (Bezanilla et al, 1997, Motegi et al, 1997, 2000Mulvihill et al, 2000).…”

Roles of a Fimbrin and an α-Actinin-like Protein in Fission Yeast Cell Polarization and Cytokinesis

“…However, one significant difference is in the relative importance of the actomyosin contractile ring during cytokinesis. Although myosin II and the contractile ring are essential for cytokinesis in S. pombe (Bezanilla et al, 1997;Kitayama et al, 1997;May et al, 1997;Motegi et al, 1997), they are not essential in S. cerevisiae (Bi et al, 1998;Lippincott and Li, 1998). A possible explanation for this difference is that the primary role of the contractile ring is to guide septum deposition (Hales et al, 1999;Vallen et al, 2000) and that the need for such guidance is greater in forming the ϳ3-m-diameter septum in S. pombe than in forming the ϳ1-m-diameter septum in S. cerevisiae.…”