The Fission Yeast Nup107-120 Complex Functionally Interacts with the Small GTPase Ran/Spi1 and Is Required for mRNA Export, Nuclear Pore Distribution, and Proper Cell Division

Abstract

We have characterized Schizosaccharomyces pombe open reading frames encoding potential orthologues of constituents of the evolutionarily conserved Saccharomyces cerevisiae Nup84 vertebrate Nup107-160 nuclear pore subcomplex, namely Nup133a, Nup133b, Nup120, Nup107, Nup85, and Seh1. In spite of rather weak sequence conservation, in vivo analyses demonstrated that these S. pombe proteins are localized at the nuclear envelope. Biochemical data confirmed the organization of these nucleoporins within conserved complexes. Although examination of the S. cerevisiae and S. pombe deletion mutants revealed different viability phenotypes, functional studies indicated that the involvement of this complex in nuclear pore distribution and mRNA export has been conserved between these highly divergent yeasts. Unexpectedly, microscopic analyses of some of the S. pombe mutants revealed cell division defects at the restrictive temperature (abnormal septa and mitotic spindles and chromosome missegregation) that were reminiscent of defects occurring in several S. pombe GTPase Ran (Ran^Sp)/Spi1 cycle mutants. Furthermore, deletion of nup120 moderately altered the nuclear location of Ran^Sp/Spi1, whereas overexpression of a nonfunctional Ran^Sp/Spi1-GFP allele was specifically toxic in the Δnup120 and Δnup133b mutant strains, indicating a functional and genetic link between constituents of the S. pombe Nup107-120 complex and of the Ran^Sp/Spi1 pathway.

We thank U. Fleig (Institut fuer Mikrobiologie, Duesseldorf, Germany), K. Tatebayashi (Institute of Medical Science, University of Tokyo, Tokyo, Japan), T. Toda (Cancer Research UK, London, United Kingdom), M. Yanagida (Kyoto University, Kyoto, Japan), R. Dhar (National Cancer Institute, National Institutes of Health, Bethesda, Md.), and K. Gull (University of Manchester, Manchester, United Kingdom), for generous gifts of strains, plasmids, and antibodies; I. Tratner and G. Baldacci (Institut Curie, Orsay, France) and B. Arcangioli (Institut Pasteur, Paris, France) for strains, advice, and help with FACS analyses; D. Tenza and J. B. Sibarita (Institut Curie, Paris, France) for thin-section electron microscopy and deconvolution microscopy; P. E. Gleizes (LBME, Toulouse, France) for help with 25S rRNA FISH experiments; N. Ong (Baylor College of Medicine, Houston, Tex.) for technical assistance; and the members of the A. Paoletti (Institut Curie, Paris, France) and V. Doye laboratories for discussions and critical reading of the manuscript.

V.D. was funded by the Institut Curie, the Centre National de la Recherche Scientifique, the Association pour la Recherche contre le Cancer, and La Ligue Contre le Cancer (Comité de Paris). S. W. Baï and J. Rouquette were supported by the French Ministry for Research and Technology and La Ligue contre le Cancer, respectively. S.S. and M.U. were funded by the National Institutes of Health (GM49119).