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

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.
Mesh Terms:
Amino Acid Sequence, Animals, Cloning, Molecular, Cyclin B, Cyclins, DNA, Fungal, Fungal Proteins, Ligases, Mitosis, Molecular Sequence Data, Mutation, Oocytes, S Phase, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Ubiquitin-Conjugating Enzymes, Xenopus
Nature
Date: Jan. 05, 1995
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