Phosphorylation of the myosin-II light chain does not regulate the timing of cytokinesis in fission yeast.
Proper coordination of cytokinesis with chromosome separation during mitosis is crucial to ensure that each daughter cell inherits an equivalent set of chromosomes. It has been proposed that one mechanism by which this is achieved is through temporally regulated myosin regulatory light chain (RLC) phosphorylation (Satterwhite, L. L., and Pollard, T. D. (1992) Curr. Opin. Cell Biol. 4, 43-52). A variety of evidence is consistent with this model. A direct test of the importance of RLC phosphorylation in vivo has been done only in Dictyostelium and Drosophila; phosphorylation of the RLC is essential in Drosophila (Jordan, P., and Karess, R. (1997) J. Cell Biol. 139, 1805-1819) but not essential in Dictyostelium (Ostrow, B. D., Chen, P., and Chisholm, R. L. (1994) J. Cell Biol. 127, 1945-1955). The Schizosaccharomyces pombe myosin light chain Cdc4p is essential for cytokinesis, but it was unknown whether phosphorylation played a role in its regulation. Here we show that the S. pombe myosin light chain Cdc4p is phosphorylated in vivo on either serine 2 or 6 but not both. Mutation of either or both of these sites to alanine did not effect the ability of Cdc4p to bind the type II myosin Myo2p, and cells expressing only these mutated versions of Cdc4p grew and divided normally. Similarly, mutation of Ser-2, Ser-6, or both residues to aspartic acid did not affect growth or division of cells. Thus we conclude that phosphorylation of Cdc4p is not essential in vivo for the function of the protein.
McCollum
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Howard Hughes Medical Institute and Department of Cell Biology, Vanderbilt University School of Medicine, Nashville Tennessee 37232, USA.
Feoktistova
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A
Gould
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KL
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division; D002875:Chromosomes / Q000378:metabolism; D003598:Cytoskeletal Proteins; D044783:F-Box Proteins; D005656:Fungal Proteins; D008938:Mitosis; D008969:Molecular Sequence Data; D009154:Mutation; D018995:Myosin Heavy Chains; D024462:Myosin Type II; D024701:Myosin Type V; D009218:Myosins / Q000235:genetics / Q000378:metabolism*; D010748:Phosphopeptides / Q000032:analysis; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000378:metabolism / Q000502:physiology*; D029702:Schizosaccharomyces pombe Proteins; D044767:Ubiquitin-Protein Ligases
D001426:Bacterial Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; D044783:F-Box Proteins; D005656:Fungal Proteins; C077512:MYO2 protein, S cerevisiae; C434211:MYO2 protein, S pombe; D010748:Phosphopeptides; D010750:Phosphoproteins; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; C513274:cdc4 protein, S pombe; D044767:Ubiquitin-Protein Ligases; D024462:Myosin Type II; D024701:Myosin Type V; D018995:Myosin Heavy Chains; D009218:Myosins