Abstract
Cyclin B is degraded at the onset of anaphase by a ubiquitin-dependent proteolytic system. We have fractionated mitotic Xenopus egg extracts to identify components required for this process. We find that UBC4 and at least one other ubiquitin-conjugating enzyme can support cyclin B ubiquitination. The mitotic specificity of cyclin ubiquitination is determined by a 20S complex that contains homologs of budding yeast CDC16 and CDC27. Because these proteins are required for anaphase in yeast and mammalian cells, we refer to this complex as the anaphase-promoting complex (APC). CDC27 antibodies deplete APC activity, while immunopurified CDC27 complexes are sufficient to complement either interphase extracts or a mixture of recombinant UBC4 and the ubiquitin-activating enzyme E1. These results suggest that APC functions as a regulated ubiquitin-protein ligase that targets cyclin B for destruction in mitosis.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Anaphase / physiology
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Animals
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Apc3 Subunit, Anaphase-Promoting Complex-Cyclosome
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Apc6 Subunit, Anaphase-Promoting Complex-Cyclosome
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Cell Cycle Proteins / metabolism*
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Cyclins / metabolism*
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Ligases / analysis
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Ligases / genetics
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Ligases / metabolism
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Macromolecular Substances
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Mitosis / physiology*
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Ovum
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Recombinant Proteins / pharmacology
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Saccharomyces cerevisiae Proteins
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Subcellular Fractions / metabolism
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Ubiquitin-Activating Enzymes
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Ubiquitin-Conjugating Enzymes
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Ubiquitin-Protein Ligases
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Ubiquitins / metabolism*
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Xenopus
Substances
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Apc3 Subunit, Anaphase-Promoting Complex-Cyclosome
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Apc6 Subunit, Anaphase-Promoting Complex-Cyclosome
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CDC16 protein, S cerevisiae
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CDC27 protein, S cerevisiae
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Cell Cycle Proteins
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Cyclins
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Macromolecular Substances
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Recombinant Proteins
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Saccharomyces cerevisiae Proteins
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Ubiquitins
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Ubiquitin-Conjugating Enzymes
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ubiquitin-conjugating enzyme UBC4
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Ubiquitin-Protein Ligases
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Ligases
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Ubiquitin-Activating Enzymes