Role of a ubiquitin-conjugating enzyme in degradation of S- and M-phase cyclins

Nature. 1995 Jan 5;373(6509):78-81. doi: 10.1038/373078a0.


Cell cycle progression in eukaryotes is controlled by the p34cdc2/CDC28 protein kinase and its short-lived, phase-specific regulatory subunits called cyclins. In Xenopus oocytes, degradation of M-phase (B-type) cyclins is required for exit from mitosis and is mediated by the ubiquitin-dependent proteolytic system. Here we show that B-type-cyclin degradation in yeast involves an essential nuclear ubiquitin-conjugating enzyme, UBC9. Repression of UBC9 synthesis prevents cell cycle progression at the G2 or early M phase, causing the accumulation of large budded cells with a single nucleus, a short spindle and replicated DNA. In ubc9 mutants both CLB5, an S-phase cyclin, and CLB2, an M-phase cyclin, are stabilized. In wild-type cells the CLB5 protein is unstable throughout the cell cycle, whereas CLB2 turnover occurs only at a specific cell-cycle stage. Thus distinct degradation signals or regulated interaction with the ubiquitin-protein ligase system may determine the cell-cycle specificity of cyclin proteolysis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cloning, Molecular
  • Cyclin B*
  • Cyclins / metabolism*
  • DNA, Fungal
  • Fungal Proteins / genetics*
  • Fungal Proteins / metabolism
  • Ligases / genetics*
  • Mitosis*
  • Molecular Sequence Data
  • Mutation
  • Oocytes
  • S Phase*
  • Saccharomyces cerevisiae / enzymology*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae Proteins*
  • Ubiquitin-Conjugating Enzymes*
  • Xenopus


  • CLB5 protein, S cerevisiae
  • Cyclin B
  • Cyclins
  • DNA, Fungal
  • Fungal Proteins
  • Saccharomyces cerevisiae Proteins
  • Ubiquitin-Conjugating Enzymes
  • Ligases
  • ubiquitin-conjugating enzyme UBC9

Associated data

  • GENBANK/X82538