title: Regulation of cell cycle transcription factor Swi5 by karyopherin Msn5.
abstract: Inactivation of S. cerevisiae β-karyopherin Msn5 causes hypersensitivity to the overexpression of mitotic cyclin Clb2 and aggravates growth defects of many mutant strains in mitotic exit, suggesting a connection between Msn5 and mitotic exit. We determined that Msn5 controlled subcellular localization of the mitotic exit transcription factor Swi5, since it was required for Swi5 nuclear export. Msn5 physically interacted with the N-terminal end of Swi5. Inactivation of Msn5 caused a severe reduction in cellular levels of Swi5 protein. This effect occurred by a post-transcriptional mechanism, since SWI5 mRNA levels were not affected. The reduced amount of Swi5 in msn5 mutant cells was not due to an increased protein degradation rate, but to a defect in Swi5 synthesis. Despite the change in localization and protein level, Swi5-regulated transcription was not defective in the msn5 mutant strain. However, a high level of Swi5 was toxic in the absence of Msn5. This deleterious effect was eliminated when Swi5 nuclear import was abrogated, suggesting that nuclear export by Msn5 is important for cell physiology, because it prevents toxic Swi5 nuclear accumulation.
authors.affiliation: Deparament de Bioquimica i Biologia Molecular, Universitat de Valencia, Valencia, Spain.
authors.forename: Francisco José
authors.initials: FJ
authors.lastname: Taberner
authors.forename: Inma
authors.initials: I
authors.lastname: Quilis
authors.forename: Josep
authors.initials: J
authors.lastname: Sendra
authors.forename: María Carmen
authors.initials: MC
authors.lastname: Bañó
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Igual
mesh_terms: D021581:Active Transport, Cell Nucleus; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D005800:Genes, Fungal / Q000235:genetics; D028884:Karyopherins / Q000378:metabolism*; D008938:Mitosis; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D055550:Protein Stability; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D014157:Transcription Factors / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D028884:Karyopherins; C401306:MSN5 protein, S cerevisiae; C080218:SWI5 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors