SUMO conjugation and deconjugation.
Ligation of the ubiquitin-like protein SUMO (Smt3p) to other proteins is essential for viability of the yeast Saccharomyces cerevisiae. Like ubiquitin (Ub), SUMO undergoes ATP-dependent activation by a specific activating enzyme. SUMO-activating enzyme is a heterodimer composed of Uba2p and Aos1p, polypeptides with sequence similarities, respectively, to the C- and N-terminal parts of Ub-activating enzyme. To study the function of SUMO conjugation, we isolated uba2 mutants that were temperature-sensitive for growth. In these mutants conjugation of SUMO to other proteins was drastically reduced, even at the temperature permissive for growth. In a screen for spontaneous suppressors of the temperature-sensitive growth phenotype of the mutant uha2-ts9, we isolated a strain with a null mutation (sut9) in a gene of hitherto unknown function (SUT9/YIL031W/SMT4). This gene encodes a protein with similarities to Ulp1p, a dual-function protease that processes the SUMO precursor and deconjugates SUMO from its substrates. The novel protein was therefore termed Ulp2p. Inactivation of ULP2 in a strain expressing wild-type SUMO-activating enzyme resulted in slow and temperature-sensitive growth, and accumulation of SUMO conjugates. Thus, mutations in SUMO-activating enzyme and mutations in Ulp2p suppress each other, indicating that SUMO conjugation and deconjugation must be in balance for cells to grow normally. Other phenotypes of ulp2 mutants include a defect in cell cycle progression, hypersensitivity to DNA damage, and chromosome mis-segregation. Ulp2p is predominantly located within the nucleus, whereas Ulp1p colocalizes with nuclear pore complex proteins, indicating that the apparently distinct functions of the two SUMO deconjugating enzymes are spatially separated.
Schwienhorst
I
I
Institute for Genetics, University of Cologne, Germany.
Johnson
E S
ES
Dohmen
R J
RJ
D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D004249:DNA Damage; D004271:DNA, Fungal / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D006801:Humans; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009685:Nuclear Envelope / Q000378:metabolism; D010641:Phenotype; D025842:SUMO-1 Protein; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013489:Suppression, Genetic; D013696:Temperature; D044764:Ubiquitin-Activating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D004271:DNA, Fungal; D005656:Fungal Proteins; D025842:SUMO-1 Protein; C470301:UBA2 protein, human; D014452:Ubiquitins; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; D044764:Ubiquitin-Activating Enzymes