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Mol. Cell. Biol., Sep 1997, 5530-5539, Vol 17, No. 9
N Larsson, U Marklund, HM Gradin, G Brattsand and M Gullberg
Oncoprotein 18 (Op18; also termed p19, 19K, metablastin, stathmin, and
prosolin) is a conserved protein that regulates microtubule (MT) dynamics.
Op18 is multisite phosphorylated on four Ser residues during mitosis; two
of these Ser residues, Ser-25 and Ser-38, are targets for cyclin-dependent
protein kinases (CDKs), and the other two Ser residues, Ser-16 and Ser-63,
are targets for an unidentified protein kinase. Mutations of the two CDK
sites have recently been shown to result in a mitotic block caused by
destabilization of MTs. To understand the role of Op18 in regulation of MT
dynamics during mitosis, in this study we dissected the functions of all
four phosphorylation sites of Op18 by combining genetic, morphological, and
biochemical analyses. The data show that all four phosphorylation sites are
involved in switching off Op18 activity during mitosis, an event that
appears to be essential for formation of the spindle during metaphase.
However, the mechanisms by which specific sites down- regulate Op18
activity differ. Hence, dual phosphorylation on the CDK sites Ser-25 and
Ser-38 appears to be required for phosphorylation of Ser-16 and Ser-63;
however, by themselves, the CDK sites are of only minor importance in
direct regulation of Op18 activity. Subsequent phosphorylation of either
Ser-16, Ser-63, or both efficiently switches off Op18 activity.
Copyright © 1997, American Society for Microbiology
Control of microtubule dynamics by oncoprotein 18: dissection of the regulatory role of multisite phosphorylation during mitosis
Department for Cell and Molecular Biology, University of Umea, Sweden.
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