title: The Saccharomyces cerevisiae checkpoint genes RAD9, CHK1 and PDS1 are required for elevated homologous recombination in a mec1 (ATR) hypomorphic mutant.
abstract: Specific ataxia telangiectasia and Rad3-related (ATR) mutations confer higher frequencies of homologous recombination. The genetic requirements for hyper-recombination in ATR mutants are unknown. MEC1, the essential yeast ATR/ATM homolog, controls S and G(2) checkpoints and the DNA damage-inducibility of genes after radiation exposure. Since the mec1-Delta (null) mutant is defective in both S and G(2) checkpoints, we measured spontaneous and DNA damage-associated sister chromatid exchange (SCE), homolog (heteroallelic) recombination, and homology-directed translocations in the mec1-21 hypomorphic mutant, which is defective in the S phase checkpoint but retains some G(2) checkpoint function. We observed a sixfold, tenfold and 30-fold higher rate of spontaneous SCE, heteroallelic recombination, and translocations, respectively, in mec1-21 mutants compared to wild type. The mec1-21 hyper-recombination was partially reduced in rad9, pds1 and chk1 mutants, and abolished in rad52 mutants, suggesting the hyper-recombination results from RAD52-dependent recombination pathway(s) that require G(2) checkpoint functions. The HU and UV sensitivities of mec1-21 rad9 and mec1-21 rad52 were synergistically increased, compared to the single mutants, indicating that mec1-21, rad52 and rad9 mutants are defective in independent pathways for HU and UV resistance. G(2)-arrested mec1-21 rad9 cells exhibit more UV resistance than non-synchronized cells, indicating that one function of RAD9 in conferring UV resistance in mec1-21 is by triggering G(2) arrest. We suggest that checkpoint genes that function in the RAD9-mediated pathway are required for either homologous recombination or DNA damage resistance in the S phase checkpoint mutant mec1-21.
authors.affiliation: Ordway Research Institute, Albany, New York 12208, USA. mfasullo@ordwayresearch.org
authors.forename: Michael
authors.initials: M
authors.lastname: Fasullo
authors.forename: Mingzeng
authors.initials: M
authors.lastname: Sun
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology*; D000071877:Checkpoint Kinase 1; D016195:G2 Phase / Q000235:genetics; D018816:Genes, cdc / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D008954:Models, Biological; D050505:Mutant Proteins / Q000235:genetics / Q000502:physiology; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D030781:Organisms, Genetically Modified; D010641:Phenotype; D011494:Protein Kinases / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D051721:Rad52 DNA Repair and Recombination Protein / Q000502:physiology; D011995:Recombination, Genetic / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000502:physiology*; D064249:Securin; D017385:Sequence Homology
chemical_list: D018797:Cell Cycle Proteins; D047908:Intracellular Signaling Peptides and Proteins; D050505:Mutant Proteins; D009687:Nuclear Proteins; C578004:PDS1 protein, S cerevisiae; C497197:RAD52 protein, S cerevisiae; D051721:Rad52 DNA Repair and Recombination Protein; D029701:Saccharomyces cerevisiae Proteins; D064249:Securin; C069930:rad9 protein; D011494:Protein Kinases; D000071877:Checkpoint Kinase 1; C088937:MEC1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases