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Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To understand how cytokinesis is regulated during mitosis, we tested cyclin-p34cdc2 for myosin-II kinase activity, and investigated the mitotic-specific phosphorylation of myosin-II in lysates of Xenopus eggs. Purified cyclin-p34cdc2 phosphorylated the regulatory light chain of cytoplasmic and smooth muscle myosin-II in vitro on serine-1 or serine-2 and threonine-9, sites known to inhibit the actin-activated myosin ATPase activity of smooth muscle and nonmuscle myosin (Nishikawa, M., J. R. Sellers, R. S. Adelstein, and H. Hidaka. 1984. J. Biol. Chem. 259:8808-8814; Bengur, A. R., A. E. Robinson, E. Appella, and J. R. Sellers. 1987. J. Biol. Chem. 262:7613-7617; Ikebe, M., and S. Reardon. 1990. Biochemistry. 29:2713-2720). Serine-1 or -2 of the regulatory light chain of Xenopus cytoplasmic myosin-II was also phosphorylated in Xenopus egg lysates stabilized in metaphase, but not in interphase. Inhibition of myosin-II by cyclin-p34cdc2 during prophase and metaphase could delay cytokinesis until chromosome segregation is initiated and thus determine the timing of cytokinesis relative to earlier events in mitosis.
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PMID:Phosphorylation of myosin-II regulatory light chain by cyclin-p34cdc2: a mechanism for the timing of cytokinesis. 138 67

A calmodulin-independent kinase isolated from chicken intestinal brush border phosphorylates brush border myosin mainly at an apparently single threonine on its 20 kDa light chains. Phosphorylation to 1.9 mol phosphate/mol myosin activated the myosin actin-activated ATPase about 12-fold, to about 100 nmol/min per mg. Brush border myosin ATPase can thus be activated by phosphorylation either at threonine, by calmodulin-independent kinase, or at serine, by calmodulin-dependent myosin light chain kinase, as previously shown [(1987) FEBS Lett. 223, 262-266].
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PMID:Phosphorylation of brush border myosin at threonine on its 20 kDa light chains by a calmodulin-independent kinase activates its ATPase. 296 28

The Drosophila spaghetti squash (sqh) gene encodes the regulatory myosin light chain (RMLC) of nonmuscle myosin II. Biochemical analysis of vertebrate nonmuscle and smooth muscle myosin II has established that phosphorylation of certain amino acids of the RMLC greatly increases the actin-dependent myosin ATPase and motor activity of myosin in vitro. We have assessed the in vivo importance of these sites, which in Drosophila correspond to serine-21 and threonine-20, by creating a series of transgenes in which these specific amino acids were altered. The phenotypes of the transgenes were examined in an otherwise null mutant background during oocyte development in Drosophila females. Germ line cystoblasts entirely lacking a functional sqh gene show severe defects in proliferation and cytokinesis. The ring canals, cytoplasmic bridges linking the oocyte to the nurse cells in the egg chamber, are abnormal, suggesting a role of myosin II in their establishment or maintenance. In addition, numerous aggregates of myosin heavy chain accumulate in the sqh null cells. Mutant sqh transgene sqh-A20, A21 in which both serine-21 and threonine-20 have been replaced by alanines behaves in most respects identically to the null allele in this system, with the exception that no heavy chain aggregates are found. In contrast, expression of sqh-A21, in which only the primary phosphorylation target serine-21 site is altered, partially restores functionality to germ line myosin II, allowing cystoblast division and oocyte development, albeit with some cytokinesis failure, defects in the rapid cytoplasmic transport from nurse cells to cytoplasm characteristic of late stage oogenesis, and some damaged ring canals. Substituting a glutamate for the serine-21 (mutant sqh-E21) allows oogenesis to be completed with minimal defects, producing eggs that can develop normally to produce fertile adults. Flies expressing sqh-A20, in which only the secondary phosphorylation site is absent, appear to be entirely wild type. Taken together, this genetic evidence argues that phosphorylation at serine-21 is critical to RMLC function in activating myosin II in vivo, but that the function can be partially provided by phosphorylation at threonine-20.
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PMID:Myosin light chain-activating phosphorylation sites are required for oogenesis in Drosophila. 941 74

The Rho-associated kinases ROCK I and ROCK II are serine/threonine kinases that play central and critical roles in regulating the actin cytoskeleton. Activation of ROCK proteins contributes positively to the phosphorylation of myosin II light chains (MLC), myosin ATPase activity, stabilization of filamentous actin, and coupling of the actin-myosin filaments to the plasma membrane, thereby leading to the increased actin-myosin force generation and contractility. We have constructed a conditionally-activated form of ROCK II (called ROCK:ER) by fusing the ROCK II kinase domain to the estrogen receptor hormone-binding domain. In this chapter, we describe the construction and characterization of this regulatable ROCK:ER fusion protein.
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PMID:Conditional regulation of a ROCK-estrogen receptor fusion protein. 1647 86