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* Cell Biology of Development and Differentiation Group, ABL Basic Research Program, National Cancer Institute, Frederick
Cancer Research and Development Center, Frederick, Maryland 21702-1201; and We describe a novel mammalian protein kinase related to two newly identified yeast and fly kinases
Department of Microbiology, University of
Texas, Austin, Texas 78712
Ipl1 and aurora, respectively
mutations in
which cause disruption of chromosome segregation. We
have designated this kinase as Ipl1- and aurora-related
kinase 1 (IAK1). IAK1 expression in mouse fibroblasts
is tightly regulated temporally and spatially during the
cell cycle. Transcripts first appear at G1/S boundary, are
elevated at M-phase, and disappear rapidly after completion of mitosis. The protein levels and kinase activity of IAK1 are also cell cycle regulated with a peak at
M-phase. IAK1 protein has a distinct subcellular and
temporal pattern of localization. It is first identified on
the centrosomes immediately after the duplicated centrosomes have separated. The protein remains on the
centrosome and the centrosome-proximal part of the
spindle throughout mitosis and is detected weakly on
midbody microtubules at telophase and cytokinesis. In
cells recovering from nocodazole treatment and in
taxol-treated mitotic cells, IAK1 is associated with microtubule organizing centers. A wild-type and a mutant form of IAK1 cause mitotic spindle defects and lethality in ipl1 mutant yeast cells but not in wild-type cells,
suggesting that IAK1 interferes with Ipl1p function in
yeast. Taken together, these data strongly suggest that
IAK1 may have an important role in centrosome and/
or spindle function during chromosome segregation in
mammalian cells. We suggest that IAK1 is a new member of an emerging subfamily of the serine/threonine
kinase superfamily. The members of this subfamily may
be important regulators of chromosome segregation.
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