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Identification and characterization of new elements involved in checkpoint and feedback controls in fission yeast
F al-Khodairy1, E Fotou, K S Sheldrick
1MRC Cell Mutation Unit, Sussex University, Falmer, United Kingdom.
Abstract:
To investigate the mechanisms that ensure the dependency relationships between cell cycle events and to investigate the checkpoints that prevent progression through the cell cycle after DNA damage, we have isolated mutants defective in the checkpoint and feedback control pathways. We report the isolation and characterization of 11 new loci that define distinct classes of mutants defective in one or more of the checkpoint and feedback control pathways. Two mutants, rad26.T12 and rad27.T15, were selected for molecular analysis. The null allele of the rad26 gene (rad26.d) shares the phenotype reported for the "checkpoint rad" mutants rad1, rad3, rad9, rad17, and hus1, which are defective in the radiation checkpoint and in the feedback controls that ensure the order of cell cycle events. The null allele of the rad27 gene (rad27.d) defines a new class of Schizosaccharomyces pombe mutant. The rad27 complementing gene codes for a putative protein kinase that is required for cell cycle arrest after DNA damage but not for the feedback control that links mitosis to the completion of prior DNA synthesis (the same gene has recently been described by Walworth et al. (1993) as chk1). These properties are similar to those of the rad9 gene of Saccharomyces cerevisiae. A comparative analysis of the radiation responses in rad26.d, rad26.T12, and rad27.d cells has revealed the existence of two separable responses to DNA damage controlled by the "checkpoint rad" genes. The first, G2 arrest, is defective in rad27.d and rad26.d but is unaffected in rad26.T12 cells. The second response is not associated with G2 arrest after DNA damage and is defective in rad26.d and rad26.T12 but not rad27.d cells. A study of the radiation sensitivity of these mutants through the cell cycle suggests that this second response is associated with S phase and that the checkpoint rad mutants, in addition to an inability to arrest mitosis after radiation, are defective in an S phase radiation checkpoint.
Insights
Researchers identified new fission yeast mutants (rad26 and rad27) essential for cell cycle checkpoints and DNA damage response, revealing distinct roles in cell cycle control and DNA repair pathways.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Cell cycle progression is tightly regulated by checkpoints to maintain genomic stability.
- DNA damage triggers specific checkpoints to prevent cell division until repairs are complete.
- Understanding these regulatory mechanisms is crucial for comprehending cell cycle control and disease.
Purpose of the Study:
- To investigate the mechanisms ensuring cell cycle event dependency.
- To identify checkpoints preventing cell cycle progression after DNA damage.
- To isolate and characterize mutants defective in checkpoint and feedback control pathways.
Main Methods:
- Isolation and characterization of 11 new fission yeast (Schizosaccharomyces pombe) mutant loci.
- Molecular analysis of two mutants: rad26.T12 and rad27.T15.
- Comparative analysis of radiation responses in rad26.d, rad26.T12, and rad27.d cells.
Main Results:
- Identified 11 new loci defining distinct checkpoint and feedback control mutants.
- rad26 null allele (rad26.d) exhibits defects in radiation checkpoint and cell cycle order.
- rad27 null allele (rad27.d) defines a new class, with the gene encoding a protein kinase (Chk1) involved in DNA damage-induced cell cycle arrest.
Conclusions:
- Two separable DNA damage responses exist: G2 arrest (defective in rad27.d, rad26.d) and an S-phase-associated response (defective in rad26.d, rad26.T12).
- Checkpoint rad mutants are defective in both mitotic arrest and an S-phase radiation checkpoint.
- rad27 (Chk1) is essential for G2 arrest, while rad26 is involved in both G2 and S-phase checkpoints.