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Molecular and Cellular Biology, January 2000, p. 286-298, Vol. 20, No. 1
Laboratory of
Metabolism1 and Laboratory of
Experimental Carcinogenesis,3 Division of Basic
Sciences, National Cancer Institute, National Institutes of Health,
Bethesda, Maryland 20892, and Department of Molecular and
Cellular Biology, Harvard University, Cambridge, Massachusetts
021382
Received 2 August 1999/Returned for modification 9 September
1999/Accepted 4 October 1999
Members of the polo subfamily of protein kinases play pivotal roles
in cell proliferation. In addition to the kinase domain, polo kinases
have a strikingly conserved sequence in the noncatalytic C-terminal
domain, termed the polo box. Here we show that the budding-yeast polo
kinase Cdc5, when fused to green fluorescent protein and expressed
under its endogenous promoter, localizes at spindle poles and the
mother bud neck. Overexpression of Cdc5 can induce a class of cells
with abnormally elongated buds in a polo box- and kinase
activity-dependent manner. In addition to localizing at the spindle
poles and cytokinetic neck filaments, Cdc5 induces and localizes to
additional septin ring structures within the elongated buds. Without
impairing kinase activity, conservative mutations in the polo box
abolish the ability of Cdc5 to functionally complement the defect
associated with a cdc5-1 temperature-sensitive mutation, to
localize to the spindle poles and cytokinetic neck filaments, and to
induce elongated cells with ectopic septin ring structures. Consistent
with the polo box-dependent subcellular localization, the C-terminal
domain of Cdc5, but not its polo box mutant, is sufficient for
subcellular localization, and its overexpression appears to inhibit
cytokinesis. These data provide evidence that the polo box is required
to direct Cdc5 to specific subcellular locations and induce or organize cytokinetic structures.
0270-7306/0/$04.00+0
Essential Function of the Polo Box of Cdc5 in
Subcellular Localization and Induction of Cytokinetic
Structures
*
Corresponding author. Mailing address: Laboratory of
Metabolism, Division of Basic Sciences, National Cancer Institute,
National Institutes of Health, 9000 Rockville Pike, Bldg. 37, Rm. 3D25, Bethesda, MD 20892. Phone: (301) 435-8894. Fax: (301) 496-8419. E-mail:
kyunglee{at}pop.nci.nih.gov.
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