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Pluta AJ, Studniarek C, Murphy S, Norbury CJ. Cyclin-dependent kinases: Masters of the eukaryotic universe. WILEY INTERDISCIPLINARY REVIEWS. RNA 2023; 15:e1816. [PMID: 37718413 PMCID: PMC10909489 DOI: 10.1002/wrna.1816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Revised: 07/21/2023] [Accepted: 08/03/2023] [Indexed: 09/19/2023]
Abstract
A family of structurally related cyclin-dependent protein kinases (CDKs) drives many aspects of eukaryotic cell function. Much of the literature in this area has considered individual members of this family to act primarily either as regulators of the cell cycle, the context in which CDKs were first discovered, or as regulators of transcription. Until recently, CDK7 was the only clear example of a CDK that functions in both processes. However, new data points to several "cell-cycle" CDKs having important roles in transcription and some "transcriptional" CDKs having cell cycle-related targets. For example, novel functions in transcription have been demonstrated for the archetypal cell cycle regulator CDK1. The increasing evidence of the overlap between these two CDK types suggests that they might play a critical role in coordinating the two processes. Here we review the canonical functions of cell-cycle and transcriptional CDKs, and provide an update on how these kinases collaborate to perform important cellular functions. We also provide a brief overview of how dysregulation of CDKs contributes to carcinogenesis, and possible treatment avenues. This article is categorized under: RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Processing > 3' End Processing RNA Processing > Splicing Regulation/Alternative Splicing.
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Affiliation(s)
| | | | - Shona Murphy
- Sir William Dunn School of PathologyUniversity of OxfordOxfordUK
| | - Chris J. Norbury
- Sir William Dunn School of PathologyUniversity of OxfordOxfordUK
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2
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Liang P, Lister K, Yates L, Argunhan B, Zhang X. Phosphoregulation of DNA repair via the Rad51 auxiliary factor Swi5-Sfr1. J Biol Chem 2023; 299:104929. [PMID: 37330173 PMCID: PMC10366545 DOI: 10.1016/j.jbc.2023.104929] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Revised: 06/06/2023] [Accepted: 06/07/2023] [Indexed: 06/19/2023] Open
Abstract
Homologous recombination (HR) is a major pathway for the repair of DNA double-strand breaks, the most severe form of DNA damage. The Rad51 protein is central to HR, but multiple auxiliary factors regulate its activity. The heterodimeric Swi5-Sfr1 complex is one such factor. It was previously shown that two sites within the intrinsically disordered domain of Sfr1 are critical for the interaction with Rad51. Here, we show that phosphorylation of five residues within this domain regulates the interaction of Swi5-Sfr1 with Rad51. Biochemical reconstitutions demonstrated that a phosphomimetic mutant version of Swi5-Sfr1 is defective in both the physical and functional interaction with Rad51. This translated to a defect in DNA repair, with the phosphomimetic mutant yeast strain phenocopying a previously established interaction mutant. Interestingly, a strain in which Sfr1 phosphorylation was blocked also displayed sensitivity to DNA damage. Taken together, we propose that controlled phosphorylation of Sfr1 is important for the role of Swi5-Sfr1 in promoting Rad51-dependent DNA repair.
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Affiliation(s)
- Pengtao Liang
- Section of Structural and Synthetic Biology, Faculty of Medicine, Imperial College London, London, UK
| | - Katie Lister
- Section of Structural and Synthetic Biology, Faculty of Medicine, Imperial College London, London, UK
| | - Luke Yates
- Section of Structural and Synthetic Biology, Faculty of Medicine, Imperial College London, London, UK
| | - Bilge Argunhan
- Section of Structural and Synthetic Biology, Faculty of Medicine, Imperial College London, London, UK.
| | - Xiaodong Zhang
- Section of Structural and Synthetic Biology, Faculty of Medicine, Imperial College London, London, UK.
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3
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Ohtsuka H, Sakata H, Kitazaki Y, Tada M, Shimasaki T, Otsubo Y, Maekawa Y, Kobayashi M, Imada K, Yamashita A, Aiba H. The ecl family gene ecl3+ is induced by phosphate starvation and contributes to sexual differentiation in fission yeast. J Cell Sci 2023; 136:287015. [PMID: 36779416 PMCID: PMC10038150 DOI: 10.1242/jcs.260759] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Accepted: 02/07/2023] [Indexed: 02/14/2023] Open
Abstract
In Schizosaccharomyces pombe, ecl family genes are induced by several signals, such as starvation of various nutrients, including sulfur, amino acids and Mg2+, and environmental stress, including heat or oxidative stress. These genes mediate appropriate cellular responses and contribute to the maintenance of cell viability and induction of sexual differentiation. Although this yeast has three ecl family genes with overlapping functions, any environmental conditions that induce ecl3+ remain unidentified. We demonstrate that ecl3+ is induced by phosphate starvation, similar to its chromosomally neighboring genes, pho1+ and pho84+, which respectively encode an extracellular acid phosphatase and an inorganic phosphate transporter. ecl3+ expression was induced by the transcription factor Pho7 and affected by the cyclin-dependent kinase (CDK)-activating kinase Csk1. Phosphate starvation induced G1 arrest and sexual differentiation via ecl family genes. Biochemical analyses suggested that this G1 arrest was mediated by the stabilization of the CDK inhibitor Rum1, which was dependent on ecl family genes. This study shows that ecl family genes are required for appropriate responses to phosphate starvation and provides novel insights into the diversity and similarity of starvation responses.
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Affiliation(s)
- Hokuto Ohtsuka
- Laboratory of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan
| | - Hiroki Sakata
- Laboratory of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan
| | - Yuto Kitazaki
- Laboratory of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan
| | - Masanobu Tada
- Laboratory of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan
| | - Takafumi Shimasaki
- Laboratory of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan
| | - Yoko Otsubo
- Interdisciplinary Research Unit, National Institute for Basic Biology, Okazaki, Aichi 444-858, Japan
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
- Center for Novel Science Initiatives, National Institutes of Natural Sciences, Okazaki, Aichi 444-8585, Japan
| | - Yasukichi Maekawa
- Laboratory of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan
| | - Mikuto Kobayashi
- Laboratory of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan
| | - Kazuki Imada
- Department of Chemistry and Biochemistry, National Institute of Technology (KOSEN), Suzuka College, Suzuka 510-0294, Japan
- Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
| | - Akira Yamashita
- Interdisciplinary Research Unit, National Institute for Basic Biology, Okazaki, Aichi 444-858, Japan
- Center for Low-temperature Plasma Sciences, Nagoya University, Nagoya, Aichi 464-8603, Japan
| | - Hirofumi Aiba
- Laboratory of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan
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4
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Olson CM, Liang Y, Leggett A, Park WD, Li L, Mills CE, Elsarrag SZ, Ficarro SB, Zhang T, Düster R, Geyer M, Sim T, Marto JA, Sorger PK, Westover KD, Lin CY, Kwiatkowski N, Gray NS. Development of a Selective CDK7 Covalent Inhibitor Reveals Predominant Cell-Cycle Phenotype. Cell Chem Biol 2019; 26:792-803.e10. [PMID: 30905681 DOI: 10.1016/j.chembiol.2019.02.012] [Citation(s) in RCA: 99] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2018] [Revised: 12/19/2018] [Accepted: 02/18/2019] [Indexed: 02/06/2023]
Abstract
Cyclin-dependent kinase 7 (CDK7) regulates both cell cycle and transcription, but its precise role remains elusive. We previously described THZ1, a CDK7 inhibitor, which dramatically inhibits superenhancer-associated gene expression. However, potent CDK12/13 off-target activity obscured CDK7s contribution to this phenotype. Here, we describe the discovery of a highly selective covalent CDK7 inhibitor. YKL-5-124 causes arrest at the G1/S transition and inhibition of E2F-driven gene expression; these effects are rescued by a CDK7 mutant unable to covalently engage YKL-5-124, demonstrating on-target specificity. Unlike THZ1, treatment with YKL-5-124 resulted in no change to RNA polymerase II C-terminal domain phosphorylation; however, inhibition could be reconstituted by combining YKL-5-124 and THZ531, a selective CDK12/13 inhibitor, revealing potential redundancies in CDK control of gene transcription. These findings highlight the importance of CDK7/12/13 polypharmacology for anti-cancer activity of THZ1 and posit that selective inhibition of CDK7 may be useful for treatment of cancers marked by E2F misregulation.
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Affiliation(s)
- Calla M Olson
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biology Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA; Therapeutic Innovation Center (THINC@BCM), Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA; Verna & Marrs McLean Department of Biochemistry & Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Yanke Liang
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biology Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA
| | - Alan Leggett
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biology Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA
| | - Woojun D Park
- Department of Molecular & Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Lianbo Li
- Departments of Biochemistry and Radiation Oncology, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, USA
| | - Caitlin E Mills
- Laboratory of Systems Pharmacology, Harvard Medical School, Boston MA 02115, USA
| | - Selma Z Elsarrag
- Department of Molecular & Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Scott B Ficarro
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biology Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA; Blais Proteomics Center, Dana-Farber Cancer Institute, Boston, MA 02115, USA
| | - Tinghu Zhang
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biology Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA
| | - Robert Düster
- Institute of Structural Biology, University of Bonn, Sigmund-Freud-Strasse 25, 53127 Bonn, Germany
| | - Matthias Geyer
- Institute of Structural Biology, University of Bonn, Sigmund-Freud-Strasse 25, 53127 Bonn, Germany
| | - Taebo Sim
- Chemical Kinomics Research Center, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea; KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-701, Korea
| | - Jarrod A Marto
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biology Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA; Blais Proteomics Center, Dana-Farber Cancer Institute, Boston, MA 02115, USA
| | - Peter K Sorger
- Laboratory of Systems Pharmacology, Harvard Medical School, Boston MA 02115, USA
| | - Ken D Westover
- Departments of Biochemistry and Radiation Oncology, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, USA
| | - Charles Y Lin
- Therapeutic Innovation Center (THINC@BCM), Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA; Verna & Marrs McLean Department of Biochemistry & Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA; Department of Molecular & Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Nicholas Kwiatkowski
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biology Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA.
| | - Nathanael S Gray
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biology Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA.
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Sansó M, Lee KM, Viladevall L, Jacques PÉ, Pagé V, Nagy S, Racine A, St. Amour CV, Zhang C, Shokat KM, Schwer B, Robert F, Fisher RP, Tanny JC. A positive feedback loop links opposing functions of P-TEFb/Cdk9 and histone H2B ubiquitylation to regulate transcript elongation in fission yeast. PLoS Genet 2012; 8:e1002822. [PMID: 22876190 PMCID: PMC3410854 DOI: 10.1371/journal.pgen.1002822] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Accepted: 05/24/2012] [Indexed: 11/25/2022] Open
Abstract
Transcript elongation by RNA polymerase II (RNAPII) is accompanied by conserved patterns of histone modification. Whereas histone modifications have established roles in transcription initiation, their functions during elongation are not understood. Mono-ubiquitylation of histone H2B (H2Bub1) plays a key role in coordinating co-transcriptional histone modification by promoting site-specific methylation of histone H3. H2Bub1 also regulates gene expression through an unidentified, methylation-independent mechanism. Here we reveal bidirectional communication between H2Bub1 and Cdk9, the ortholog of metazoan positive transcription elongation factor b (P-TEFb), in the fission yeast Schizosaccharomyces pombe. Chemical and classical genetic analyses indicate that lowering Cdk9 activity or preventing phosphorylation of its substrate, the transcription processivity factor Spt5, reduces H2Bub1 in vivo. Conversely, mutations in the H2Bub1 pathway impair Cdk9 recruitment to chromatin and decrease Spt5 phosphorylation. Moreover, an Spt5 phosphorylation-site mutation, combined with deletion of the histone H3 Lys4 methyltransferase Set1, phenocopies morphologic and growth defects due to H2Bub1 loss, suggesting independent, partially redundant roles for Cdk9 and Set1 downstream of H2Bub1. Surprisingly, mutation of the histone H2B ubiquitin-acceptor residue relaxes the Cdk9 activity requirement in vivo, and cdk9 mutations suppress cell-morphology defects in H2Bub1-deficient strains. Genome-wide analyses by chromatin immunoprecipitation also demonstrate opposing effects of Cdk9 and H2Bub1 on distribution of transcribing RNAPII. Therefore, whereas mutual dependence of H2Bub1 and Spt5 phosphorylation indicates positive feedback, mutual suppression by cdk9 and H2Bub1-pathway mutations suggests antagonistic functions that must be kept in balance to regulate elongation. Loss of H2Bub1 disrupts that balance and leads to deranged gene expression and aberrant cell morphologies, revealing a novel function of a conserved, co-transcriptional histone modification. Modification of histone proteins is an important transcriptional regulatory mechanism in eukaryotic cells. Although various histone modifications are found primarily within the coding regions of transcribed genes, how they influence transcription elongation remains unclear. Among these modifications is mono-ubiquitylation of histone H2B (H2Bub1), which is needed for co-transcriptional methylation of histone H3 at specific sites. Here we show that H2Bub1 and Cdk9, the kinase component of positive transcription elongation factor b (P-TEFb), are jointly regulated by a positive feedback loop: Cdk9 activity is needed for co-transcriptional H2Bub1, and H2Bub1 in turn stimulates Cdk9 activity toward one of its major substrates, the conserved elongation factor Spt5. We provide genetic evidence that the combined action of H2Bub1 on Spt5 phosphorylation and histone methylation accounts for the gene-regulatory effects of this modification. Surprisingly, our genetic and genome-wide studies indicate that P-TEFb and H2Bub1 act in opposition on elongating RNA polymerase. We suggest that the positive feedback linking P-TEFb and H2Bub1 helps to maintain a balance between their opposing actions. These results highlight a novel regulatory role for a conserved histone modification during transcription elongation.
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Affiliation(s)
- Miriam Sansó
- Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Karen M. Lee
- Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Laia Viladevall
- Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, New York, United States of America
| | | | - Viviane Pagé
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Canada
| | - Stephen Nagy
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Canada
| | - Ariane Racine
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Canada
| | - Courtney V. St. Amour
- Programs in Biochemistry, Cell and Molecular Biology, Weill Cornell Medical College, New York, New York, United States of America
| | - Chao Zhang
- Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, California, United States of America
| | - Kevan M. Shokat
- Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, California, United States of America
| | - Beate Schwer
- Department of Microbiology and Immunology, Weill Cornell Medical College, New York, New York, United States of America
| | - François Robert
- Institut de Recherches Cliniques de Montréal, Montréal, Canada
| | - Robert P. Fisher
- Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, New York, United States of America
- * E-mail: (RPF); (JCT)
| | - Jason C. Tanny
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Canada
- * E-mail: (RPF); (JCT)
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6
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Abstract
Cyclin-dependent kinase 9 (CDK9), with its cyclin T regulatory subunit, is a component of the positive transcription elongation factor b (P-TEFb) complex, which stimulates transcription elongation and also functions in co-transcriptional histone modification, mRNA processing, and mRNA export. CDK9 also binds to cyclin K but the function of this CDK9-cyclin K complex is less clear. We and others have recently shown that CDK9 functions directly in maintaining genome integrity. This activity is restricted to CDK9-cyclin K. Depletion of CDK9 or its cyclin K but not cyclin T regulatory subunit impairs cell cycle recovery in response to replication stress and induces spontaneous DNA damage in replicating cells. CDK9-cyclin K also interacts with ATR and other DNA damage response and DNA repair proteins. CDK9 accumulates on chromatin and limits the amount of single-stranded DNA in response to replication stress. Collectively, these data are consistent with a model in which CDK9 responds to replication stress by localizing to chromatin to reduce the breakdown of stalled replication forks and promote recovery from replication arrest. The direct role of CDK9-cyclin K in pathways that maintain genome integrity in response to replication stress appear to be evolutionarily conserved.
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Affiliation(s)
- David S Yu
- Department of Radiation Oncology, Emory University School of Medicine, Atlanta, GA, USA.
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Yu DS, Zhao R, Hsu EL, Cayer J, Ye F, Guo Y, Shyr Y, Cortez D. Cyclin-dependent kinase 9-cyclin K functions in the replication stress response. EMBO Rep 2010; 11:876-82. [PMID: 20930849 DOI: 10.1038/embor.2010.153] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Revised: 08/13/2010] [Accepted: 08/31/2010] [Indexed: 11/09/2022] Open
Abstract
Cyclin-dependent kinase 9 (CDK9) is a well-characterized subunit of the positive transcription elongation factor b complex in which it regulates transcription elongation in cooperation with cyclin T. However, CDK9 also forms a complex with cyclin K, the function of which is less clear. Using a synthetic lethal RNA interference screen in human cells, we identified CDK9 as a component of the replication stress response. Loss of CDK9 activity causes an increase in spontaneous levels of DNA damage signalling in replicating cells and a decreased ability to recover from a transient replication arrest. This activity is restricted to CDK9-cyclin K complexes and is independent of CDK9-cyclin T complex. CDK9 accumulates on chromatin in response to replication stress and limits the amount of single-stranded DNA in cells under stress. Furthermore, we show that CDK9 and cyclin K interact with ataxia telangiectasia and Rad3-related protein and other checkpoint signalling proteins. These results reveal an unexpectedly direct role for CDK9-cyclin K in checkpoint pathways that maintain genome integrity in response to replication stress.
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Affiliation(s)
- David S Yu
- Department of Radiation Oncology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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Behind the wheel and under the hood: functions of cyclin-dependent kinases in response to DNA damage. DNA Repair (Amst) 2009; 8:1018-24. [PMID: 19464967 DOI: 10.1016/j.dnarep.2009.04.009] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cell division and the response to genotoxic stress are intimately connected in eukaryotes, for example, by checkpoint pathways that signal the presence of DNA damage or its ongoing repair to the cell cycle machinery, leading to reversible arrest or apoptosis. Recent studies reveal another connection: the cyclin-dependent kinases (CDKs) that govern both DNA synthesis (S) phase and mitosis directly coordinate DNA repair processes with progression through the cell cycle. In both mammalian cells and yeast, the two major modes of double strand break (DSB) repair--homologous recombination (HR) and non-homologous end joining (NHEJ)--are reciprocally regulated during the cell cycle. In yeast, the cell cycle kinase Cdk1 directly promotes DSB repair by HR during the G2 phase. In mammalian cells, loss of Cdk2, which is active throughout S and G2 phases, results in defective DNA damage repair and checkpoint signaling. Here we provide an overview of data that implicate CDKs in the regulation of DNA damage responses in yeast and metazoans. In yeast, CDK activity is required at multiple points in the HR pathway; the precise roles of CDKs in mammalian HR have yet to be determined. Finally, we consider how the two different, and in some cases opposing, roles of CDKs--as targets of negative regulation by checkpoint signaling and as positive effectors of repair pathway selection and function--could be balanced to produce a coordinated and effective response to DNA damage.
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