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J. Cell Biol.,
Volume 141, Number 7, June 29, 1998 1563-1574
* Department of Molecular Biology, Sciences II, University of Geneva, CH-1211 Geneva 4, Switzerland; and Nek2 (for NIMA-related kinase 2) is a mammalian cell cycle-regulated kinase structurally related
to the mitotic regulator NIMA of Aspergillus nidulans.
In human cells, Nek2 associates with centrosomes, and
overexpression of active Nek2 has drastic consequences
for centrosome structure. Here, we describe the molecular characterization of a novel human centrosomal
protein, C-Nap1 (for centrosomal Nek2-associated protein 1), first identified as a Nek2-interacting protein in a
yeast two-hybrid screen. Antibodies raised against recombinant C-Nap1 produced strong labeling of centrosomes by immunofluorescence, and immunoelectron
microscopy revealed that C-Nap1 is associated specifically with the proximal ends of both mother and daughter centrioles. On Western blots, anti-C-Nap1 antibodies recognized a large protein (>250 kD) that was
highly enriched in centrosome preparations. Sequencing of overlapping cDNAs showed that C-Nap1 has a
calculated molecular mass of 281 kD and comprises extended domains of predicted coiled-coil structure.
Whereas C-Nap1 was concentrated at centrosomes in
all interphase cells, immunoreactivity at mitotic spindle
poles was strongly diminished. Finally, the COOH-terminal domain of C-Nap1 could readily be phosphorylated by Nek2 in vitro, as well as after coexpression of
the two proteins in vivo. Based on these findings, we
propose a model implicating both Nek2 and C-Nap1 in
the regulation of centriole-centriole cohesion during
the cell cycle.
Max-Planck-Institut für Biologie, Abteilung Membranbiochemie, D-72076 Tübingen, Germany
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