Interplay of replication checkpoints and repair proteins at stalled replication forks.
TL;DR: This review focuses mainly on the results obtained in budding yeast on the multiple roles of checkpoints in maintaining fork integrity and on the enzymatic activities that cooperate with the checkpoint pathway to promote fork resumption and repair of DNA lesions thereby contributing to genome integrity.
About: This article is published in DNA Repair.The article was published on 2007-07-01. It has received 144 citations till now. The article focuses on the topics: Control of chromosome duplication & DNA re-replication.
Citations
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TL;DR: Oncogene-induced DNA damage may explain two key features of cancer: genomic instability and the high frequency of p53 mutations.
Abstract: Of all types of DNA damage, DNA double-strand breaks (DSBs) pose the greatest challenge to cells. One might have, therefore, anticipated that a sizable number of DNA DSBs would be incompatible with cell proliferation. Yet recent experimental findings suggest that, in both precancerous lesions and cancers, activated oncogenes induce stalling and collapse of DNA replication forks, which in turn leads to formation of DNA DSBs. This continuous formation of DNA DSBs may contribute to the genomic instability that characterizes the vast majority of human cancers. In addition, in precancerous lesions, these DNA DSBs activate p53, which, by inducing apoptosis or senescence, raises a barrier to tumor progression. Breach of this barrier by various mechanisms, most notably by p53 mutations, that impair the DNA damage response pathway allows cancers to develop. Thus, oncogene-induced DNA damage may explain two key features of cancer: genomic instability and the high frequency of p53 mutations.
1,714 citations
TL;DR: This work has witnessed an explosion in understanding of DNA damage sensing, signaling, and the complex interplay between protein phosphorylation and the ubiquitin pathway employed by the DDR network to execute the response to DNA damage.
1,639 citations
Cites background from "Interplay of replication checkpoint..."
...…for proteins involved in DNA replication, such as the MCMs, ORCs, RFC, GINS, TopBP1, and DNA polymerase complexes, which could go a long way toward explaining how fork stability and slowing of DNA replication are controlled in response to damage (Branzei and Foiani, 2007; Lambert et al., 2007)....
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...These studies revealed a very strong enrichment for proteins involved in DNA replication, such as the MCMs, ORCs, RFC, GINS, TopBP1, and DNA polymerase complexes, which could go a long way toward explaining how fork stability and slowing of DNA replication are controlled in response to damage (Branzei and Foiani, 2007; Lambert et al., 2007)....
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TL;DR: HR accessory factors that facilitate other stages of the Rad51- and Dmc1-catalyzed homologous DNA pairing and strand exchange reaction have also been identified.
Abstract: Homologous recombination (HR) serves to eliminate deleterious lesions, such as double-stranded breaks and interstrand crosslinks, from chromosomes. HR is also critical for the preservation of repli- cation forks, for telomere maintenance, and chromosome segrega- tion in meiosis I. As such, HR is indispensable for the maintenance of genome integrity and the avoidance of cancers in humans. The HR reaction is mediated by a conserved class of enzymes termed recombinases. Two recombinases, Rad51 and Dmc1, catalyze the pairing and shuffling of homologous DNA sequences in eukaryotic cells via a filamentous intermediate on ssDNA called the presynaptic filament. The assembly of the presynaptic filament is a rate-limiting process that is enhanced by recombination mediators, such as the breast tumor suppressor BRCA2. HR accessory factors that facil- itate other stages of the Rad51- and Dmc1-catalyzed homologous DNA pairing and strand exchange reaction have also been identified. Recent progress on elucidating the mechanisms of action of Rad51 and Dmc1 and their cohorts of ancillary factors is reviewed here.
1,542 citations
TL;DR: The repair of DNA lesions that occur endogenously or in response to diverse genotoxic stresses is indispensable for genome integrity and has provided insights into the mechanisms that contribute to DNA repair in specific cell-cycle phases.
Abstract: The repair of DNA lesions that occur endogenously or in response to diverse genotoxic stresses is indispensable for genome integrity. DNA lesions activate checkpoint pathways that regulate specific DNA-repair mechanisms in the different phases of the cell cycle. Checkpoint-arrested cells resume cell-cycle progression once damage has been repaired, whereas cells with unrepairable DNA lesions undergo permanent cell-cycle arrest or apoptosis. Recent studies have provided insights into the mechanisms that contribute to DNA repair in specific cell-cycle phases and have highlighted the mechanisms that ensure cell-cycle progression or arrest in normal and cancerous cells.
1,132 citations
TL;DR: The XRCC3 protein, which is required for RAD51 foci formation, is also required for replication restart of HU-stalled forks, suggesting that RAD51-mediated strand invasion supports fork restart.
740 citations
Cites background from "Interplay of replication checkpoint..."
...It has been proposed that eukaryotic forks might not necessarily need to restart because replication can be completed from adjacent origins (Branzei and Foiani, 2007; Paulsen and Cimprich, 2007)....
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References
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TL;DR: It is shown that UBC9, a small ubiquitin-related modifier (SUMO)-conjugating enzyme, is also affiliated with this pathway and that proliferating cell nuclear antigen (PCNA) is a substrate, and that damage-induced PCNA ubiquitination is elementary for DNA repair and occurs at the same conserved residue in yeast and humans.
Abstract: The RAD6 pathway is central to post-replicative DNA repair in eukaryotic cells; however, the machinery and its regulation remain poorly understood. Two principal elements of this pathway are the ubiquitin-conjugating enzymes RAD6 and the MMS2-UBC13 heterodimer, which are recruited to chromatin by the RING-finger proteins RAD18 and RAD5, respectively. Here we show that UBC9, a small ubiquitin-related modifier (SUMO)-conjugating enzyme, is also affiliated with this pathway and that proliferating cell nuclear antigen (PCNA) -- a DNA-polymerase sliding clamp involved in DNA synthesis and repair -- is a substrate. PCNA is mono-ubiquitinated through RAD6 and RAD18, modified by lysine-63-linked multi-ubiquitination--which additionally requires MMS2, UBC13 and RAD5--and is conjugated to SUMO by UBC9. All three modifications affect the same lysine residue of PCNA, suggesting that they label PCNA for alternative functions. We demonstrate that these modifications differentially affect resistance to DNA damage, and that damage-induced PCNA ubiquitination is elementary for DNA repair and occurs at the same conserved residue in yeast and humans.
2,182 citations
TL;DR: This review encompasses different aspects of DSB-induced recombination in Saccharomyces and attempts to relate genetic, molecular biological, and biochemical studies of the processes of DNA repair and recombination.
Abstract: The budding yeast Saccharomyces cerevisiae has been the principal organism used in experiments to examine genetic recombination in eukaryotes. Studies over the past decade have shown that meiotic recombination and probably most mitotic recombination arise from the repair of double-strand breaks (DSBs). There are multiple pathways by which such DSBs can be repaired, including several homologous recombination pathways and still other nonhomologous mechanisms. Our understanding has also been greatly enriched by the characterization of many proteins involved in recombination and by insights that link aspects of DNA repair to chromosome replication. New molecular models of DSB-induced gene conversion are presented. This review encompasses these different aspects of DSB-induced recombination in Saccharomyces and attempts to relate genetic, molecular biological, and biochemical studies of the processes of DNA repair and recombination.
2,175 citations
TL;DR: It is shown that mutations in BLM and hTOPO IIIα together effect the resolution of a recombination intermediate containing a double Holliday junction and prevents exchange of flanking sequences, which has wider implications for the understanding of the process of homologous recombination and the mechanisms that exist to prevent tumorigenesis.
Abstract: Mutations in BLM, which encodes a RecQ helicase, give rise to Bloom's syndrome, a disorder associated with cancer predisposition and genomic instability. A defining feature of Bloom's syndrome is an elevated frequency of sister chromatid exchanges. These arise from crossing over of chromatid arms during homologous recombination, a ubiquitous process that exists to repair DNA double-stranded breaks and damaged replication forks. Whereas crossing over is required in meiosis, in mitotic cells it can be associated with detrimental loss of heterozygosity. BLM forms an evolutionarily conserved complex with human topoisomerase IIIalpha (hTOPO IIIalpha), which can break and rejoin DNA to alter its topology. Inactivation of homologues of either protein leads to hyper-recombination in unicellular organisms. Here, we show that BLM and hTOPO IIIalpha together effect the resolution of a recombination intermediate containing a double Holliday junction. The mechanism, which we term double-junction dissolution, is distinct from classical Holliday junction resolution and prevents exchange of flanking sequences. Loss of such an activity explains many of the cellular phenotypes of Bloom's syndrome. These results have wider implications for our understanding of the process of homologous recombination and the mechanisms that exist to prevent tumorigenesis.
1,082 citations
TL;DR: The cellular response to DSBs and DNA replication stress is likely directed by the Mre11 complex detecting and processing DNA ends in conjunction with Sae2 and by RP-A recognizing single-stranded DNA and recruiting additional checkpoint and repair proteins.
938 citations
TL;DR: Oligonucleotide microarrays were used to map the detailed topography of chromosome replication in the budding yeast Saccharomyces cerevisiae, finding the two ends of each of the 16 chromosomes are highly correlated in their times of replication.
Abstract: Oligonucleotide microarrays were used to map the detailed topography of chromosome replication in the budding yeast Saccharomyces cerevisiae. The times of replication of thousands of sites across the genome were determined by hybridizing replicated and unreplicated DNAs, isolated at different times in S phase, to the microarrays. Origin activations take place continuously throughout S phase but with most firings near mid-S phase. Rates of replication fork movement vary greatly from region to region in the genome. The two ends of each of the 16 chromosomes are highly correlated in their times of replication. This microarray approach is readily applicable to other organisms, including humans.
850 citations