Fission Yeast Mog1p Homologue, Which Interacts With the Small GTPase Ran, Is Required for Mitosis-to-Interphase Transition and poly(A)+ RNA Metabolism

Fission Yeast Mog1p Homologue, Which Interacts With the Small GTPase Ran, Is Required for Mitosis-to-Interphase Transition and poly(A)⁺ RNA Metabolism

K. Tatebayashi^a, T. Tani^b,c, and H. Ikeda^a,d
^a Department of Molecular Biology, Institute of Medical Science, the University of Tokyo, P.O. Takanawa, Tokyo 108-8639, Japan,
^b Department of Biology, Graduate School of Science, Kyushu University, Fukuoka 812-8581, Japan,
^c PRESTO, Japan Science and Technology Corporation, Fukuoka 812-8581, Japan
^d Microbial Chemistry, Center for Basic Research, The Kitasato Institute, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8642, Japan

Corresponding author: K. Tatebayashi, Department of Molecular Biology, Institute of Medical Science, the University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan., tategone{at}ims.u-tokyo.ac.jp (E-mail)

Communicating editor: F. WINSTON

We have cloned and characterized the Schizosaccharomyces pombegene mog1⁺, which encodes a protein with homology to the Saccharomycescerevisiae Mog1p participating in the Ran-GTPase system. TheS. pombe Mog1p is predominantly localized in the nucleus. Incontrast to the S. cerevisiae MOG1 gene, the S. pombe mog1⁺gene is essential for cell viability. mog1⁺ is required forthe mitosis-to-interphase transition, as the mog1-1 mutant arrestsat restrictive temperatures as septated, binucleated cells withhighly condensed chromosomes and an aberrant nuclear envelope.FACS analysis showed that these cells do not undergo a subsequentround of DNA replication. Surprisingly, also unlike the ${Delta}$ mog1mutation in S. cerevisiae, the mog1-1 mutation causes nucleolaraccumulation of poly(A)⁺ RNA at the restrictive temperaturein S. pombe, but the signals do not overlap with the fibrillarin-richregion of the nucleolus. Thus, we found that mog1⁺ is requiredfor the mitosis-to-interphase transition and a class of RNAmetabolism. In our attempt to identify suppressors of mog1-1,we isolated the spi1⁺ gene, which encodes the fission yeasthomologue of Ran. We found that overexpression of Spi1p rescuesthe S. pombe ${Delta}$ mog1 cells from death. On the basis of these results,we conclude that mog1⁺ is involved in the Ran-GTPase system.

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