title: Suppressors of cdc25p overexpression identify two pathways that influence the G2/M checkpoint in fission yeast.
abstract: Checkpoints maintain the order of cell-cycle events. At G2/M, a checkpoint blocks mitosis in response to damaged or unreplicated DNA. There are significant differences in the checkpoint responses to damaged DNA and unreplicated DNA, although many of the same genes are involved in both responses. To identify new genes that function specifically in the DNA replication checkpoint pathway, we searched for high-copy suppressors of overproducer of Cdc25p (OPcdc25(+)), which lacks a DNA replication checkpoint. Two classes of suppressors were isolated. One class includes a new gene encoding a putative DEAD box helicase, suppressor of uncontrolled mitosis (sum3(+)). This gene negatively regulates the cell-cycle response to stress when overexpressed and restores the checkpoint response by a mechanism that is independent of Cdc2p tyrosine phosphorylation. The second class includes chk1(+) and the two Schizosaccharomyces pombe 14-3-3 genes, rad24(+) and rad25(+), which appear to suppress the checkpoint defect by inhibiting Cdc25p. We show that rad24Delta mutants are defective in the checkpoint response to the DNA replication inhibitor hydroxyurea at 37 degrees and that cds1Delta rad24Delta mutants, like cds1Delta chk1Delta mutants, are entirely checkpoint deficient at 29 degrees. These results suggest that chk1(+) and rad24(+) may function redundantly with cds1(+) in the checkpoint response to unreplicated DNA.
authors.affiliation: Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Forbes
authors.forename: T
authors.initials: T
authors.lastname: Humphrey
authors.forename: T
authors.initials: T
authors.lastname: Enoch
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000502:physiology; D000071877:Checkpoint Kinase 1; D064447:Checkpoint Kinase 2; D004265:DNA Helicases / Q000235:genetics; D004261:DNA Replication / Q000235:genetics; D004271:DNA, Fungal / Q000096:biosynthesis / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics* / Q000502:physiology; D016195:G2 Phase / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal; D006918:Hydroxyurea / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008938:Mitosis / Q000235:genetics*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D012568:Schizosaccharomyces / Q000187:drug effects / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins; D015398:Signal Transduction; D014158:Transcription, Genetic; D014443:Tyrosine / Q000378:metabolism; D020666:ras-GRF1
chemical_list: D018797:Cell Cycle Proteins; D004271:DNA, Fungal; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D029702:Schizosaccharomyces pombe Proteins; C501114:rad24 protein, S pombe; C489574:rad25 protein, S pombe; D020666:ras-GRF1; D014443:Tyrosine; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C578636:Cds1 protein, S pombe; D000071877:Checkpoint Kinase 1; C000605873:Chk1 protein, S pombe; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase; D004265:DNA Helicases; D006918:Hydroxyurea