Abstract
Cdt1, a protein essential in G1 for licensing of origins for DNA replication, is inhibited in S-phase, both by binding to geminin and degradation by proteasomes. Cdt1 is also degraded after DNA damage to stop licensing of new origins until after DNA repair. Phosphorylation of Cdt1 by cyclin-dependent kinases promotes its binding to SCF-Skp2 E3 ubiquitin ligase, but the Cdk2/Skp2-mediated pathway is not essential for the degradation of Cdt1. Here we show that the N terminus of Cdt1 contains a second degradation signal that is active after DNA damage and in S-phase and is dependent on the interaction of Cdt1 with proliferating cell nuclear antigen (PCNA) through a PCNA binding motif. The degradation involves N-terminal ubiquitination and requires Cul4 and Ddb1 proteins, components of an E3 ubiquitin ligase implicated in protein degradation after DNA damage. Therefore PCNA, the matchmaker for many proteins involved in DNA and chromatin metabolism, also serves to promote the targeted degradation of associated proteins in S-phase or after DNA damage.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Cell Cycle Proteins / genetics
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Cell Cycle Proteins / metabolism*
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Cell Cycle Proteins / radiation effects
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Cell Line
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Cullin Proteins / physiology*
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Cullin Proteins / radiation effects
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DNA Damage / physiology
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DNA-Binding Proteins / physiology*
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DNA-Binding Proteins / radiation effects
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HCT116 Cells
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Humans
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Mutagenesis, Site-Directed
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Neoplasm Proteins / genetics
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Neoplasm Proteins / physiology*
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Neoplasm Proteins / radiation effects
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Peptide Fragments / genetics
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Peptide Fragments / metabolism*
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Peptide Fragments / radiation effects
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Proliferating Cell Nuclear Antigen / physiology*
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Proliferating Cell Nuclear Antigen / radiation effects
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S Phase / genetics
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S Phase / physiology
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S Phase / radiation effects
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SKP Cullin F-Box Protein Ligases / physiology
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Ubiquitin / metabolism*
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Ultraviolet Rays
Substances
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CDT1 protein, human
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CUL4A protein, human
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Cell Cycle Proteins
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Cullin Proteins
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DDB1 protein, human
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DNA-Binding Proteins
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Neoplasm Proteins
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Peptide Fragments
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Proliferating Cell Nuclear Antigen
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Ubiquitin
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SKP Cullin F-Box Protein Ligases