When overexpressed, a novel centrosomal protein, RanBPM, causes ectopic microtubule nucleation similar to gamma-tubulin.

A novel human protein with a molecular mass of 55 kD, designated RanBPM, was isolated with the two-hybrid method using Ran as a bait. Mouse and hamster RanBPM possessed a polypeptide identical to the human one. Furthermore, Saccharomyces cerevisiae was found to have a gene, YGL227w, the COOH-terminal half of ...
which is 30% identical to RanBPM. Anti-RanBPM antibodies revealed that RanBPM was localized within the centrosome throughout the cell cycle. Overexpression of RanBPM produced multiple spots which were colocalized with gamma-tubulin and acted as ectopic microtubule nucleation sites, resulting in a reorganization of microtubule network. RanBPM cosedimented with the centrosomal fractions by sucrose- density gradient centrifugation. The formation of microtubule asters was inhibited not only by anti- RanBPM antibodies, but also by nonhydrolyzable GTP-Ran. Indeed, RanBPM specifically interacted with GTP-Ran in two-hybrid assay. The central part of asters stained by anti-RanBPM antibodies or by the mAb to gamma-tubulin was faded by the addition of GTPgammaS-Ran, but not by the addition of anti-RanBPM anti- bodies. These results provide evidence that the Ran-binding protein, RanBPM, is involved in microtubule nucleation, thereby suggesting that Ran regulates the centrosome through RanBPM.
Mesh Terms:
Adaptor Proteins, Signal Transducing, Amino Acid Sequence, Animals, CHO Cells, COS Cells, Centrosome, Cricetinae, Cytoskeletal Proteins, DNA, Complementary, Evolution, Molecular, GTP-Binding Proteins, Gene Expression, Guanosine 5'-O-(3-Thiotriphosphate), Hela Cells, Humans, Immunoblotting, Microtubules, Molecular Sequence Data, Nuclear Proteins, Tubulin, ran GTP-Binding Protein
J. Cell Biol.
Date: Nov. 16, 1998
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