Phosphorylation of the Myosin-II Light Chain Does Not Regulate the Timing of Cytokinesis in Fission Yeast*
- From the Howard Hughes Medical Institute and Department of Cell Biology, Vanderbilt University School of Medicine, Nashville Tennessee 37232
Abstract
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 inDictyostelium 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 theS. pombe myosin light chain Cdc4p is phosphorylatedin 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.
Footnotes
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↵* This work was supported by the Howard Hughes Medical Institute of which K. L. G. is an Associate Investigator.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ Supported by National Institutes of Health post-doctoral training Grant GM16145. Current address: Dept. of Molecular Genetics and Microbiology, University of Massachusetts Medical Center, Worcester, MA 01605.
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↵§ To whom correspondence should be addressed. Tel.: 615-343-9502; Fax: 615-343-0723; E-mail:kathy.gould{at}mcmail.vanderbilt.edu.
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↵2 K. Gould, unpublished observations.
- Abbreviations:
- PAGE
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polyacrylamide gel electrophoresis
- PVDF
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polyvinylidene difluoride
- HA
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hemagglutinin
- RLC
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regulatory light chain
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- Received March 1, 1999.
- Revision received April 16, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
