title: A Checkpoint-Related Function of the MCM Replicative Helicase Is Required to Avert Accumulation of RNA:DNA Hybrids during S-phase and Ensuing DSBs during G2/M.
abstract: The Mcm2-7 complex is the catalytic core of the eukaryotic replicative helicase. Here, we identify a new role for this complex in maintaining genome integrity. Using both genetic and cytological approaches, we find that a specific mcm allele (mcm2DENQ) causes elevated genome instability that correlates with the appearance of numerous DNA-damage associated foci of γH2AX and Rad52. We further find that the triggering events for this genome instability are elevated levels of RNA:DNA hybrids and an altered DNA topological state, as over-expression of either RNaseH (an enzyme specific for degradation of RNA in RNA:DNA hybrids) or Topoisomerase 1 (an enzyme that relieves DNA supercoiling) can suppress the mcm2DENQ DNA-damage phenotype. Moreover, the observed DNA damage has several additional unusual properties, in that DNA damage foci appear only after S-phase, in G2/M, and are dependent upon progression into metaphase. In addition, we show that the resultant DNA damage is not due to spontaneous S-phase fork collapse. In total, these unusual mcm2DENQ phenotypes are markedly similar to those of a special previously-studied allele of the checkpoint sensor kinase ATR/MEC1, suggesting a possible regulatory interplay between Mcm2-7 and ATR during unchallenged growth. As RNA:DNA hybrids primarily result from transcription perturbations, we suggest that surveillance-mediated modulation of the Mcm2-7 activity plays an important role in preventing catastrophic conflicts between replication forks and transcription complexes. Possible relationships among these effects and the recently discovered role of Mcm2-7 in the DNA replication checkpoint induced by HU treatment are discussed.
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Sriram
authors.initials: S
authors.lastname: Vijayraghavan
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Feng-Ling
authors.initials: FL
authors.lastname: Tsai
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Anthony
authors.identifier: 0000-0002-9664-9503
authors.initials: A
authors.lastname: Schwacha
mesh_terms: D059447:Cell Cycle Checkpoints / Q000235:genetics; D004249:DNA Damage / Q000235:genetics*; D004265:DNA Helicases / Q000235:genetics; D004261:DNA Replication / Q000235:genetics*; D042822:Genomic Instability / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D064110:Minichromosome Maintenance Proteins / Q000235:genetics*; D009154:Mutation; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D012313:RNA / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D029701:Saccharomyces cerevisiae Proteins; D012313:RNA; C088937:MEC1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D004265:DNA Helicases; D064110:Minichromosome Maintenance Proteins