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

Masafumi Nakamura, Hirohisa Masuda, Johji Horii, Kei Ichi Kuma, Nobuhiko Yokoyama, Tomoyuki Ohba, Hideo Nishitani, Takashi Miyata, Masao Tanaka, Takeharu Nishimoto

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Abstract

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 γ-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 γ- tubulin was faded by the addition of GTPγS-Ran, but not by the addition of anti-RanBPM antibodies. These results provide evidence that the Ran-binding protein, RanBPM, is involved in microtubule nucleation, thereby suggesting that Ran regulates the centrosome through RanBPM.

Original languageEnglish
Pages (from-to)1041-1052
Number of pages12
JournalJournal of Cell Biology
Volume143
Issue number4
DOIs
Publication statusPublished - Nov 16 1998

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All Science Journal Classification (ASJC) codes

  • Cell Biology

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