Regulation of nuclear proteasome by Rhp6/Ubc2 through ubiquitination and destruction of the sensor and anchor Cut8.
While proteasome is central to the degradation of cellular ubiquitinated proteins, the control of its nuclear function is barely understood. Here we show that the fission yeast ubiquitin-conjugating Rhp6/Ubc2/Rad6 and ligating enzymes Ubr1 are responsible for nuclear enrichment of proteasome through the function of Cut8, a nuclear envelope protein. Cut8 is an Rhp6 substrate that physically interacts with and tethers proteasome. Nonubiquitinatable K-all-R Cut8 weakly interacts with proteasome and fails to enrich nuclear proteasome. Consistently, the nuclear enrichment of proteasome also fails in rhp6 and ubr1 null mutants. Further, cut8 null and cut8 K-all-R mutants are hypersensitive to DNA damage, probably due to the paucity of nuclear proteasome. Thus, Rhp6 enhances the retention of nuclear proteasome through regulating Cut8. The short-lived nature of Cut8 is crucial for feedback enrichment of the proteasome within the nucleus. This is likely to be a conserved mechanism as we describe a Cut8 homolog in flies.
Takeda
Kojiro
K
Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
Yanagida
Mitsuhiro
M
D000595:Amino Acid Sequence; D000818:Animals; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D029702:Schizosaccharomyces pombe Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics / Q000378:metabolism*
D018797:Cell Cycle Proteins; C088892:Cut8 protein, S pombe; D029721:Drosophila Proteins; D029702:Schizosaccharomyces pombe Proteins; D025801:Ubiquitin; D044763:Ubiquitin-Conjugating Enzymes; C063863:rhp6 protein, S pombe; D011494:Protein Kinases; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases; D046988:Proteasome Endopeptidase Complex