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The CDK-activating kinase (CAK) Csk1 is required for normal levels of homologous recombination and resistance to DNA damage in fission yeast.

Gerber HB, Pikman Y, Fisher RP - PLoS ONE (2008)

Bottom Line: Csk1 is required for normal levels of homologous recombination (HR), and interacts genetically with components of the HR pathway.The two CAKs in fission yeast, which differ with respect to their substrate range and preferences for monomeric CDKs versus CDK/cyclin complexes as substrates, also support different functions of the CDK network in vivo.Csk1 plays a non-redundant role in safeguarding genomic integrity.

View Article: PubMed Central - PubMed

Affiliation: Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York, USA.

ABSTRACT

Background: Cyclin-dependent kinases (CDKs) perform essential roles in cell division and gene expression in all eukaryotes. The requirement for an upstream CDK-activating kinase (CAK) is also universally conserved, but the fission yeast Schizosaccharomyces pombe appears to be unique in having two CAKs with both overlapping and specialized functions that can be dissected genetically. The Mcs6 complex--orthologous to metazoan Cdk7/cyclin H/Mat1--activates the cell-cycle CDK, Cdk1, but its non-redundant essential function appears to be in regulation of gene expression, as part of transcription factor TFIIH. The other CAK is Csk1, an ortholog of budding yeast Cak1, which activates all three essential CDKs in S. pombe--Cdk1, Mcs6 and Cdk9, the catalytic subunit of positive transcription elongation factor b (P-TEFb)--but is not itself essential.

Methodology/principal findings: Cells lacking csk1(+) are viable but hypersensitive to agents that damage DNA or block replication. Csk1 is required for normal levels of homologous recombination (HR), and interacts genetically with components of the HR pathway. Tests of damage sensitivity in csk1, mcs6 and cdk9 mutants indicate that Csk1 acts pleiotropically, through Cdk9 and at least one other target (but not through Mcs6) to preserve genomic integrity.

Conclusions/significance: The two CAKs in fission yeast, which differ with respect to their substrate range and preferences for monomeric CDKs versus CDK/cyclin complexes as substrates, also support different functions of the CDK network in vivo. Csk1 plays a non-redundant role in safeguarding genomic integrity. We propose that specialized activation pathways dependent on different CAKs might insulate CDK functions important in DNA damage responses from those capable of triggering mitosis.

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Related in: MedlinePlus

Epistasis analysis with homologous recombination genes.(A) Survival after irradiation with UV or IR of the strains: (A) wild type (JS78), csk1Δ (JS155), rhp51Δ (YP6), csk1Δ rhp51Δ (HD4-6); (B) wild type (JS78), csk1Δ (JS155), rhp54Δ (YP25), csk1Δ rhp54Δ (HD2-55). (C) Cells were streaked onto YES plates and incubated for 4 days at 30°C before being photographed. Strains: wild type (JS78), csk1Δ (JS155), rhp57Δ (YP27), csk1Δ rhp57Δ (HG123). (D) Survival after UV irradiation of the strains: wild type (JS78), csk1Δ (JS155), sfr1Δ (HG24), csk1Δ sfr1Δ (HG31).
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pone-0001492-g003: Epistasis analysis with homologous recombination genes.(A) Survival after irradiation with UV or IR of the strains: (A) wild type (JS78), csk1Δ (JS155), rhp51Δ (YP6), csk1Δ rhp51Δ (HD4-6); (B) wild type (JS78), csk1Δ (JS155), rhp54Δ (YP25), csk1Δ rhp54Δ (HD2-55). (C) Cells were streaked onto YES plates and incubated for 4 days at 30°C before being photographed. Strains: wild type (JS78), csk1Δ (JS155), rhp57Δ (YP27), csk1Δ rhp57Δ (HG123). (D) Survival after UV irradiation of the strains: wild type (JS78), csk1Δ (JS155), sfr1Δ (HG24), csk1Δ sfr1Δ (HG31).

Mentions: We tested if csk1 interacts with genes important for HR repair by epistasis analysis. The rhp51Δ csk1Δ double mutant was very slightly more sensitive to both UV and IR than was the rhp51Δ single mutant (Fig. 3A), whereas rhp54Δ was clearly epistatic to csk1Δ (Fig. 3B), suggesting a role for Csk1 in the HR repair pathway. In contrast, we observed a synthetic interaction between csk1Δ and rhp57Δ. The csk1Δ rhp57Δ double mutants grew very slowly (Fig. 3C and data not shown), suggesting compromised genomic stability even in unchallenged cells.


The CDK-activating kinase (CAK) Csk1 is required for normal levels of homologous recombination and resistance to DNA damage in fission yeast.

Gerber HB, Pikman Y, Fisher RP - PLoS ONE (2008)

Epistasis analysis with homologous recombination genes.(A) Survival after irradiation with UV or IR of the strains: (A) wild type (JS78), csk1Δ (JS155), rhp51Δ (YP6), csk1Δ rhp51Δ (HD4-6); (B) wild type (JS78), csk1Δ (JS155), rhp54Δ (YP25), csk1Δ rhp54Δ (HD2-55). (C) Cells were streaked onto YES plates and incubated for 4 days at 30°C before being photographed. Strains: wild type (JS78), csk1Δ (JS155), rhp57Δ (YP27), csk1Δ rhp57Δ (HG123). (D) Survival after UV irradiation of the strains: wild type (JS78), csk1Δ (JS155), sfr1Δ (HG24), csk1Δ sfr1Δ (HG31).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2200797&req=5

pone-0001492-g003: Epistasis analysis with homologous recombination genes.(A) Survival after irradiation with UV or IR of the strains: (A) wild type (JS78), csk1Δ (JS155), rhp51Δ (YP6), csk1Δ rhp51Δ (HD4-6); (B) wild type (JS78), csk1Δ (JS155), rhp54Δ (YP25), csk1Δ rhp54Δ (HD2-55). (C) Cells were streaked onto YES plates and incubated for 4 days at 30°C before being photographed. Strains: wild type (JS78), csk1Δ (JS155), rhp57Δ (YP27), csk1Δ rhp57Δ (HG123). (D) Survival after UV irradiation of the strains: wild type (JS78), csk1Δ (JS155), sfr1Δ (HG24), csk1Δ sfr1Δ (HG31).
Mentions: We tested if csk1 interacts with genes important for HR repair by epistasis analysis. The rhp51Δ csk1Δ double mutant was very slightly more sensitive to both UV and IR than was the rhp51Δ single mutant (Fig. 3A), whereas rhp54Δ was clearly epistatic to csk1Δ (Fig. 3B), suggesting a role for Csk1 in the HR repair pathway. In contrast, we observed a synthetic interaction between csk1Δ and rhp57Δ. The csk1Δ rhp57Δ double mutants grew very slowly (Fig. 3C and data not shown), suggesting compromised genomic stability even in unchallenged cells.

Bottom Line: Csk1 is required for normal levels of homologous recombination (HR), and interacts genetically with components of the HR pathway.The two CAKs in fission yeast, which differ with respect to their substrate range and preferences for monomeric CDKs versus CDK/cyclin complexes as substrates, also support different functions of the CDK network in vivo.Csk1 plays a non-redundant role in safeguarding genomic integrity.

View Article: PubMed Central - PubMed

Affiliation: Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York, USA.

ABSTRACT

Background: Cyclin-dependent kinases (CDKs) perform essential roles in cell division and gene expression in all eukaryotes. The requirement for an upstream CDK-activating kinase (CAK) is also universally conserved, but the fission yeast Schizosaccharomyces pombe appears to be unique in having two CAKs with both overlapping and specialized functions that can be dissected genetically. The Mcs6 complex--orthologous to metazoan Cdk7/cyclin H/Mat1--activates the cell-cycle CDK, Cdk1, but its non-redundant essential function appears to be in regulation of gene expression, as part of transcription factor TFIIH. The other CAK is Csk1, an ortholog of budding yeast Cak1, which activates all three essential CDKs in S. pombe--Cdk1, Mcs6 and Cdk9, the catalytic subunit of positive transcription elongation factor b (P-TEFb)--but is not itself essential.

Methodology/principal findings: Cells lacking csk1(+) are viable but hypersensitive to agents that damage DNA or block replication. Csk1 is required for normal levels of homologous recombination (HR), and interacts genetically with components of the HR pathway. Tests of damage sensitivity in csk1, mcs6 and cdk9 mutants indicate that Csk1 acts pleiotropically, through Cdk9 and at least one other target (but not through Mcs6) to preserve genomic integrity.

Conclusions/significance: The two CAKs in fission yeast, which differ with respect to their substrate range and preferences for monomeric CDKs versus CDK/cyclin complexes as substrates, also support different functions of the CDK network in vivo. Csk1 plays a non-redundant role in safeguarding genomic integrity. We propose that specialized activation pathways dependent on different CAKs might insulate CDK functions important in DNA damage responses from those capable of triggering mitosis.

Show MeSH
Related in: MedlinePlus