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Caf1 regulates translocation of ribonucleotide reductase by releasing nucleoplasmic Spd1-Suc22 assembly.

Takahashi S, Kontani K, Araki Y, Katada T - Nucleic Acids Res. (2007)

Bottom Line: Here, we show that Caf1, a component of the Ccr4-Not complex, is responsible for resistance of the replication stress and control of the Suc22 translocation.DNA-replication stress appears to allow Caf1 to interact with Suc22, resulting in release of the nucleoplasmic Spd1-Suc22 assembly.Taken together, these results suggest a novel function of Caf1 as a key regulator in the stress-induced RNR activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiological Chemistry, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.

ABSTRACT
Appropriate supply of deoxyribonucleotides by the ribonucleotide reductase (RNR) complex is essential for DNA replication and repair. One recent model for the RNR activation in Schizosaccharomyces pombe is translocation of the regulatory subunit Suc22 from the nucleoplasm to the cytoplasm. The RNR inhibitory protein Spd1, which retains Suc22 in the nucleoplasm, is rapidly degraded upon DNA-replication stress, resulting in release of Suc22 to form the active RNR complex in the cytoplasm. Here, we show that Caf1, a component of the Ccr4-Not complex, is responsible for resistance of the replication stress and control of the Suc22 translocation. Caf1 is required not only for the stress-induced translocation of Suc22 from nucleoplasm to cytoplasm but also for the degradation of nucleoplasmic Spd1. DNA-replication stress appears to allow Caf1 to interact with Suc22, resulting in release of the nucleoplasmic Spd1-Suc22 assembly. Taken together, these results suggest a novel function of Caf1 as a key regulator in the stress-induced RNR activation.

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Possible models for the DNA-replication stress-induced translocation of Suc22. Under no-stress conditions, there is a compartment between Caf1 and the Suc22–Spd1 complex in the nucleoplasm. When cells sense DNA-replication stress, Caf1 interacts with Suc22 to facilitate the degradation of Spd1 (scheme 1) and the translocation of Suc22 from nucleoplasm to cytoplasm (scheme 2). See Discussion for further explanation.
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Figure 7: Possible models for the DNA-replication stress-induced translocation of Suc22. Under no-stress conditions, there is a compartment between Caf1 and the Suc22–Spd1 complex in the nucleoplasm. When cells sense DNA-replication stress, Caf1 interacts with Suc22 to facilitate the degradation of Spd1 (scheme 1) and the translocation of Suc22 from nucleoplasm to cytoplasm (scheme 2). See Discussion for further explanation.

Mentions: As discussed above, the RNR activity is regulated not only by the transcription of their constituent subunits but also by the subcellular translocation of the regulated subunits. Our present results address the mechanism of this translocation (Figure 7). There may be at least two possible mechanisms, by which Caf1 promotes the Spd1–Suc22 disassembly that involves the degradation of Spd1 (scheme 1) and the translocation of Suc22 from nucleoplasm to cytoplasm (scheme 2). First, Caf1 interacts with Suc22 in a manner competitive with Spd1, which facilitates the Pcu4–Ddb1–CSN-induced degradation of Spd1 and the release of Suc22 into cytoplasm. Thus, Caf1 may have a transporter role in the Suc22 translocation. Alternatively, Caf1 may function as an activator protein associating with a component(s) of the Pcu4–Ddb1–CSN complex to enhance its degradation activity. These two models are not mutually exclusive. Our findings that Caf1 progressively associates with Suc22 after HU treatment and that the stress-induced Spd1 degradation requires Caf1 may be consistent with the first transporter model. On the other hand, a physical interaction analysis shows that Caf1 interacts with Csi1, a subunit of the CSN complex (50). Moreover, we detected a possible interaction between Caf1 and Csn1 by immunoprecipitation assay (data not shown). Immunofluorescence observations revealed that Caf1 localizes both in the nucleoplasm and in the cytoplasm and that HU exposure does not apparently alter the Caf1 localization. These observations may support the second activator model.Figure 7.


Caf1 regulates translocation of ribonucleotide reductase by releasing nucleoplasmic Spd1-Suc22 assembly.

Takahashi S, Kontani K, Araki Y, Katada T - Nucleic Acids Res. (2007)

Possible models for the DNA-replication stress-induced translocation of Suc22. Under no-stress conditions, there is a compartment between Caf1 and the Suc22–Spd1 complex in the nucleoplasm. When cells sense DNA-replication stress, Caf1 interacts with Suc22 to facilitate the degradation of Spd1 (scheme 1) and the translocation of Suc22 from nucleoplasm to cytoplasm (scheme 2). See Discussion for further explanation.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1851654&req=5

Figure 7: Possible models for the DNA-replication stress-induced translocation of Suc22. Under no-stress conditions, there is a compartment between Caf1 and the Suc22–Spd1 complex in the nucleoplasm. When cells sense DNA-replication stress, Caf1 interacts with Suc22 to facilitate the degradation of Spd1 (scheme 1) and the translocation of Suc22 from nucleoplasm to cytoplasm (scheme 2). See Discussion for further explanation.
Mentions: As discussed above, the RNR activity is regulated not only by the transcription of their constituent subunits but also by the subcellular translocation of the regulated subunits. Our present results address the mechanism of this translocation (Figure 7). There may be at least two possible mechanisms, by which Caf1 promotes the Spd1–Suc22 disassembly that involves the degradation of Spd1 (scheme 1) and the translocation of Suc22 from nucleoplasm to cytoplasm (scheme 2). First, Caf1 interacts with Suc22 in a manner competitive with Spd1, which facilitates the Pcu4–Ddb1–CSN-induced degradation of Spd1 and the release of Suc22 into cytoplasm. Thus, Caf1 may have a transporter role in the Suc22 translocation. Alternatively, Caf1 may function as an activator protein associating with a component(s) of the Pcu4–Ddb1–CSN complex to enhance its degradation activity. These two models are not mutually exclusive. Our findings that Caf1 progressively associates with Suc22 after HU treatment and that the stress-induced Spd1 degradation requires Caf1 may be consistent with the first transporter model. On the other hand, a physical interaction analysis shows that Caf1 interacts with Csi1, a subunit of the CSN complex (50). Moreover, we detected a possible interaction between Caf1 and Csn1 by immunoprecipitation assay (data not shown). Immunofluorescence observations revealed that Caf1 localizes both in the nucleoplasm and in the cytoplasm and that HU exposure does not apparently alter the Caf1 localization. These observations may support the second activator model.Figure 7.

Bottom Line: Here, we show that Caf1, a component of the Ccr4-Not complex, is responsible for resistance of the replication stress and control of the Suc22 translocation.DNA-replication stress appears to allow Caf1 to interact with Suc22, resulting in release of the nucleoplasmic Spd1-Suc22 assembly.Taken together, these results suggest a novel function of Caf1 as a key regulator in the stress-induced RNR activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiological Chemistry, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.

ABSTRACT
Appropriate supply of deoxyribonucleotides by the ribonucleotide reductase (RNR) complex is essential for DNA replication and repair. One recent model for the RNR activation in Schizosaccharomyces pombe is translocation of the regulatory subunit Suc22 from the nucleoplasm to the cytoplasm. The RNR inhibitory protein Spd1, which retains Suc22 in the nucleoplasm, is rapidly degraded upon DNA-replication stress, resulting in release of Suc22 to form the active RNR complex in the cytoplasm. Here, we show that Caf1, a component of the Ccr4-Not complex, is responsible for resistance of the replication stress and control of the Suc22 translocation. Caf1 is required not only for the stress-induced translocation of Suc22 from nucleoplasm to cytoplasm but also for the degradation of nucleoplasmic Spd1. DNA-replication stress appears to allow Caf1 to interact with Suc22, resulting in release of the nucleoplasmic Spd1-Suc22 assembly. Taken together, these results suggest a novel function of Caf1 as a key regulator in the stress-induced RNR activation.

Show MeSH
Related in: MedlinePlus