Fission yeast chk1 mutants show distinct responses to different types of DNA damaging treatments.
BACKGROUND
Chk1 kinase is activated by phosphorylation at serine-345 by Rad3 checkpoint kinase and is required for DNA damage checkpoint in late S and G2 phase of S. pombe cell cycle. We studied the ability of two chk1 mutants, chk1-1 and chk1-2, to undergo phosphorylation and to delay cell cycle progression in response to different types of DNA lesions.


RESULTS
Both the Chk1-1 and Chk1-2 mutant proteins are phosphorylated to various extents when DNA is damaged in early G2 phase of cell cycle by either UV irradiation or gamma irradiation. However, chk1-2 mutant does not delay cell cycle progression in a dose dependent manner specifically upon gamma irradiations. This defect is not associated with an important loss of survival. Furthermore, both chk1 mutants survive to Camptothecin treatment despite undetectable Chk1-1 or Chk1-2 phosphorylated forms. We show that both mutant proteins are not phosphorylated in cds1 devoid cells treated with ribonucleotide reductase inhibitor hydroxyurea or when the replisome is affected by a thermosensitive mutation in DNA polymerase delta. This inability is associated with the loss of checkpoint function. We found that an increased level of Crb2/Rhp9 protein specifically complements the defect of the chk1-1 mutant allowing Chk1-1 phosphorylation upon treatment with hydroxyurea of dcds1 cells.


CONCLUSIONS
Mutants chk1-1 and chk1-2 behave differently according to the type of lesion generated on DNA.
Francesconi
Stefania
S
Institut Curie, CNRS-UMR 2027, Centre Universitaire, Bât. 110, 91405 Orsay, France. sfrances@curie.u-psud.fr
Smeets
Monique
M
Grenon
Muriel
M
Tillit
Jeanne
J
Blaisonneau
Joël
J
Baldacci
Giuseppe
G
D000483:Alleles; D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000502:physiology; D000071877:Checkpoint Kinase 1; D004249:DNA Damage; D004271:DNA, Fungal / Q000187:drug effects; D005656:Fungal Proteins / Q000096:biosynthesis / Q000502:physiology; D006918:Hydroxyurea / Q000494:pharmacology; D009154:Mutation; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000502:physiology; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000502:physiology*; D012568:Schizosaccharomyces / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D029702:Schizosaccharomyces pombe Proteins; D013696:Temperature; D014466:Ultraviolet Rays
D018797:Cell Cycle Proteins; C109867:Crb2 protein, S pombe; D004271:DNA, Fungal; D005656:Fungal Proteins; D009687:Nuclear Proteins; D029702:Schizosaccharomyces pombe Proteins; D011494:Protein Kinases; D000071877:Checkpoint Kinase 1; C000605873:Chk1 protein, S pombe; D006918:Hydroxyurea