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Maria Jasin - One of the best experts on this subject based on the ideXlab platform.
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repair of strand breaks by Homologous Recombination
Cold Spring Harbor Perspectives in Biology, 2013Co-Authors: Maria Jasin, Rodney RothsteinAbstract:In this review, we discuss the repair of DNA double-strand breaks (DSBs) using a Homologous DNA sequence (i.e., Homologous Recombination [HR]), focusing mainly on yeast and mammals. We provide a historical context for the current view of HR and describe how DSBs are processed during HR as well as interactions with other DSB repair pathways. We discuss the enzymology of the process, followed by studies on DSB repair in living cells. Whenever possible, we cite both original articles and reviews to aid the reader for further studies.
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mitotic Homologous Recombination maintains genomic stability and suppresses tumorigenesis
Nature Reviews Molecular Cell Biology, 2010Co-Authors: Mary Ellen Moynahan, Maria JasinAbstract:Homologous Recombination maintains genome stability in mammalian mitotic cells through precise repair of DNA double-strand breaks and other lesions that occur during normal cellular metabolism and through exogenous insults. Deficiencies in genes that encode proteins involved in Homologous Recombination are associated with developmental abnormalities and tumorigenesis.
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mammalian xrcc2 promotes the repair of dna double strand breaks by Homologous Recombination
Nature, 1999Co-Authors: Roger D Johnson, Nan Liu, Maria JasinAbstract:The repair of DNA double-strand breaks is essential for cells to maintain their genomic integrity. Two major mechanisms are responsible for repairing these breaks in mammalian cells, non-Homologous end-joining (NHEJ) and Homologous Recombination (HR)1,2: the importance of the former in mammalian cells is well established3, whereas the role of the latter is just emerging. Homologous Recombination is presumably promoted by an evolutionarily conserved group of genes termed the Rad52 epistasis group4,5,6,7,8,9,10,11. An essential component of the HR pathway is the strand-exchange protein, known as RecA in bacteria8 or Rad51 in yeast6. Several mammalian genes have been implicated in repair by Homologous Recombination on the basis of their sequence homology to yeast Rad51 (ref. 11): one of these is human XRCC2 (refs 12, 13). Here we show that XRCC2 is essential for the efficient repair of DNA double-strand breaks by Homologous Recombination between sister chromatids. We find that hamster cells deficient in XRCC2 show more than a 100-fold decrease in HR induced by double-strand breaks compared with the parental cell line. This defect is corrected to almost wild-type levels by transient transfection with a plasmid expressing XRCC2. The repair defect in XRCC2 mutant cells appears to be restricted to Recombinational repair because NHEJ is normal. We conclude that XRCC2 is involved in the repair of DNA double-strand breaks by Homologous Recombination.
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expression of a site specific endonuclease stimulates Homologous Recombination in mammalian cells
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: Philippe Rouet, Fatima Smih, Maria JasinAbstract:Double-strand breaks introduced into DNA in vivo have been shown to enhance Homologous Recombination in a variety of chromosomal and extrachromosomal loci in Saccharomyces cerevisiae. To introduce double-strand breaks in DNA at defined locations in mammalian cells, we have constructed a mammalian expression vector for a modified form of I-Sce I, a yeast mitochondrial intron-encoded endonuclease with an 18-bp recognition sequence. Expression of the modified I-Sce I endonuclease in COS1 cells results in cleavage of model Recombination substrates and enhanced extrachromosomal Recombination, as assayed by chloramphenicol acetyltransferase activity and Southern blot analysis. Constitutive expression of the endonuclease in mouse 3T3 cells is not lethal, possibly due to either the lack of I-Sce I sites in the genome or sufficient repair of them. Expression of an endonuclease with such a long recognition sequence will provide a powerful approach to studying a number of molecular processes in mammalian cells, including Homologous Recombination.
Thomas Helleday - One of the best experts on this subject based on the ideXlab platform.
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spontaneous Homologous Recombination is induced by collapsed replication forks that are caused by endogenous dna single strand breaks
Molecular and Cellular Biology, 2005Co-Authors: Nasrollah Salehgohari, Thomas Helleday, Helen E Bryant, Niklas Schultz, Kayan M Parker, Tobias N CasselAbstract:Homologous Recombination is vital to repair fatal DNA damage during DNA replication. However, very little is known about the substrates or repair pathways for Homologous Recombination in mammalian cells. Here, we have compared the Recombination products produced spontaneously with those produced following induction of DNA double-strand breaks (DSBs) with the I-SceI restriction endonuclease or after stalling or collapsing replication forks following treatment with thymidine or camptothecin, respectively. We show that each lesion produces different spectra of recombinants, suggesting differential use of Homologous Recombination pathways in repair of these lesions. The spontaneous spectrum most resembled the spectra produced at collapsed replication forks formed when a replication fork runs into camptothecin-stabilized DNA single-strand breaks (SSBs) within the topoisomerase I cleavage complex. We found that camptothecin-induced DSBs and the resulting Recombination repair require replication, showing that a collapsed fork is the substrate for camptothecin-induced Recombination. An SSB repair-defective cell line, EM9 with an XRCC1 mutation, has an increased number of spontaneous gammaH2Ax and RAD51 foci, suggesting that endogenous SSBs collapse replication forks, triggering Recombination repair. Furthermore, we show that gammaH2Ax, DSBs, and RAD51 foci are synergistically induced in EM9 cells with camptothecin, suggesting that lack of SSB repair in EM9 causes more collapsed forks and more Recombination repair. Furthermore, our results suggest that two-ended DSBs are rare substrates for spontaneous Homologous Recombination in a mammalian fibroblast cell line. Interestingly, all spectra showed evidence of multiple Homologous Recombination events in 8 to 16% of clones. However, there was no increase in Homologous Recombination genomewide in these clones nor were the events dependent on each other; rather, we suggest that a first Homologous Recombination event frequently triggers a second event at the same locus in mammalian cells.
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RAD51 supports spontaneous non-Homologous Recombination in mammalian cells, but not the corresponding process induced by topoisomerase inhibitors
Nucleic acids research, 2001Co-Authors: Catherine Arnaudeau, Lorène Rozier, Christophe Cazaux, M. Defais, Dag Jenssen, Thomas HelledayAbstract:The RAD51 protein has been shown to participate in Homologous Recombination by promoting ATP-dependent Homologous pairing and strand transfer reactions. In the present study, we have investigated the possible involvement of RAD51 in non-Homologous Recombination. We demonstrate that overexpression of CgRAD51 enhances the frequency of spontaneous non-Homologous Recombination in the hprt gene of Chinese hamster cells. However, the rate of non-Homologous Recombination induced by the topoisomerase inhibitors campothecin and etoposide was not altered by overexpression of RAD51. These results indicate that the RAD51 protein may perform a function in connection with spontaneous non-Homologous Recombination that is not essential to or not rate-limiting for non-Homologous Recombination induced by camptothecin or etoposide. We discuss the possibility that the role played by RAD51 in non-Homologous Recombination observed here may not be linked to non-Homologous end-joining.
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inhibition of dna synthesis is a potent mechanism by which cytostatic drugs induce Homologous Recombination in mammalian cells
Mutation Research-dna Repair, 2000Co-Authors: Catherine Arnaudeau, Dag Jenssen, Erika Tenorio Miranda, Thomas HelledayAbstract:Recombination is a process thought to be underlying genomic instability involved in carcinogenesis. This report examines the potential of cytostatic drugs to induce intrachromosomal Homologous Recombination. In order to address this question, the hprt gene of a well-characterized mammalian cell line was employed as a unique endogenous marker for Homologous Recombination. Commonly used cytostatic drugs with different mode of action were investigated in this context, i.e. bifunctional alkylating agents, inhibitors of DNA synthesis, inhibitors of topoisomerases and a spindle poison. With the exception of the spindle poison, all these drugs were found to induce Homologous Recombination, with clear differences in their Recombination potency, which could be related to their mechanism of action. Bifunctional alkylating agents were the least efficient, whereas inhibitors of DNA synthesis were found to be the most potent inducers of Homologous Recombination. This raises the question whether these later drugs should be considered for adverse effects in cancer chemotheraphy.
Giulia B Celli - One of the best experts on this subject based on the ideXlab platform.
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ku70 stimulates fusion of dysfunctional telomeres yet protects chromosome ends from Homologous Recombination
Nature Cell Biology, 2006Co-Authors: Giulia B Celli, Eros Lazzerini Denchi, Titia De LangeAbstract:Ku70-Ku80 heterodimers promote the non-Homologous end-joining (NHEJ) of DNA breaks and, as shown here, the fusion of dysfunctional telomeres. Paradoxically, this heterodimer is also located at functional mammalian telomeres and interacts with components of shelterin, the protein complex that protects telomeres. To determine whether Ku contributes to telomere protection, we analysed Ku70(-/-) mouse cells. Telomeres of Ku70(-/-) cells had a normal DNA structure and did not activate a DNA damage signal. However, Ku70 repressed exchanges between sister telomeres - a form of Homologous Recombination implicated in the alternative lengthening of telomeres (ALT) pathway. Sister telomere exchanges occurred at approximately 15% of the chromosome ends when Ku70 and the telomeric protein TRF2 were absent. Combined deficiency of TRF2 and another NHEJ factor, DNA ligase IV, did not elicit this phenotype. Sister telomere exchanges were not elevated at telomeres with functional TRF2, indicating that TRF2 and Ku70 act in parallel to repress Recombination. We conclude that mammalian chromosome ends are highly susceptible to Homologous Recombination, which can endanger cell viability if an unequal exchange generates a critically shortened telomere. Therefore, Ku- and TRF2-mediated repression of Homologous Recombination is an important aspect of telomere protection.
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ku70 stimulates fusion of dysfunctional telomeres yet protects chromosome ends from Homologous Recombination
Nature Cell Biology, 2006Co-Authors: Giulia B Celli, Eros Lazzerini Denchi, Titia De LangeAbstract:Ku70 stimulates fusion of dysfunctional telomeres yet protects chromosome ends from Homologous Recombination
Titia De Lange - One of the best experts on this subject based on the ideXlab platform.
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ku70 stimulates fusion of dysfunctional telomeres yet protects chromosome ends from Homologous Recombination
Nature Cell Biology, 2006Co-Authors: Giulia B Celli, Eros Lazzerini Denchi, Titia De LangeAbstract:Ku70-Ku80 heterodimers promote the non-Homologous end-joining (NHEJ) of DNA breaks and, as shown here, the fusion of dysfunctional telomeres. Paradoxically, this heterodimer is also located at functional mammalian telomeres and interacts with components of shelterin, the protein complex that protects telomeres. To determine whether Ku contributes to telomere protection, we analysed Ku70(-/-) mouse cells. Telomeres of Ku70(-/-) cells had a normal DNA structure and did not activate a DNA damage signal. However, Ku70 repressed exchanges between sister telomeres - a form of Homologous Recombination implicated in the alternative lengthening of telomeres (ALT) pathway. Sister telomere exchanges occurred at approximately 15% of the chromosome ends when Ku70 and the telomeric protein TRF2 were absent. Combined deficiency of TRF2 and another NHEJ factor, DNA ligase IV, did not elicit this phenotype. Sister telomere exchanges were not elevated at telomeres with functional TRF2, indicating that TRF2 and Ku70 act in parallel to repress Recombination. We conclude that mammalian chromosome ends are highly susceptible to Homologous Recombination, which can endanger cell viability if an unequal exchange generates a critically shortened telomere. Therefore, Ku- and TRF2-mediated repression of Homologous Recombination is an important aspect of telomere protection.
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ku70 stimulates fusion of dysfunctional telomeres yet protects chromosome ends from Homologous Recombination
Nature Cell Biology, 2006Co-Authors: Giulia B Celli, Eros Lazzerini Denchi, Titia De LangeAbstract:Ku70 stimulates fusion of dysfunctional telomeres yet protects chromosome ends from Homologous Recombination
Sophia David - One of the best experts on this subject based on the ideXlab platform.
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dynamics and impact of Homologous Recombination on the evolution of legionella pneumophila
PLOS Genetics, 2017Co-Authors: Sophia David, Simon R. Harris, Pekka Marttinen, Christophe Rusniok, Carmen Buchrieser, Leonor Sanchezbuso, Timothy G. HarrisonAbstract:Legionella pneumophila is an environmental bacterium and the causative agent of Legionnaires' disease. Previous genomic studies have shown that Recombination accounts for a high proportion (>96%) of diversity within several major disease-associated sequence types (STs) of L. pneumophila. This suggests that Recombination represents a potentially important force shaping adaptation and virulence. Despite this, little is known about the biological effects of Recombination in L. pneumophila, particularly with regards to Homologous Recombination (whereby genes are replaced with alternative allelic variants). Using newly available population genomic data, we have disentangled events arising from Homologous and non-Homologous Recombination in six major disease-associated STs of L. pneumophila (subsp. pneumophila), and subsequently performed a detailed characterisation of the dynamics and impact of Homologous Recombination. We identified genomic "hotspots" of Homologous Recombination that include regions containing outer membrane proteins, the lipopolysaccharide (LPS) region and Dot/Icm effectors, which provide interesting clues to the selection pressures faced by L. pneumophila. Inference of the origin of the recombined regions showed that isolates have most frequently imported DNA from isolates belonging to their own clade, but also occasionally from other major clades of the same subspecies. This supports the hypothesis that the possibility for horizontal exchange of new adaptations between major clades of the subspecies may have been a critical factor in the recent emergence of several clinically important STs from diverse genomic backgrounds. However, acquisition of recombined regions from another subspecies, L. pneumophila subsp. fraseri, was rarely observed, suggesting the existence of a Recombination barrier and/or the possibility of ongoing speciation between the two subspecies. Finally, we suggest that multi-fragment Recombination may occur in L. pneumophila, whereby multiple non-contiguous segments that originate from the same molecule of donor DNA are imported into a recipient genome during a single episode of Recombination.
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Dynamics and impact of Homologous Recombination on the evolution of Legionella pneumophila - Fig 2
2017Co-Authors: Sophia David, Leonor Sánchez-busó, Simon R. Harris, Pekka Marttinen, Christophe Rusniok, Carmen Buchrieser, Timothy G. Harrison, Julian ParkhillAbstract:A) Homologous Recombination events detected in the ST1 lineage. A phylogenetic tree, constructed using only vertically inherited mutations, is shown on the left and the scale indicates the number of SNPs. Bootstrap values are provided in S2 Fig. Homologous Recombination events are shown by blocks adjacent to the tree, which are coloured according to the BAPS cluster from which they are predicted to have been derived (see key at the top left of panel B). The plot above shows the number of Recombination events that have affected each base in the genome using a stacked visualisation to also indicate the number of events derived from different clusters. The ten genomic regions identified as Recombination hotspots are marked at the top of the plot. B) A zoomed-in illustration of hotspot 6 in the ST1 lineage, which ranges from lpp1761 to lpp1794. As in A, the Homologous Recombination events are displayed as blocks and coloured according to the BAPS cluster from which they are predicted to be derived. The genes shown at the top of the figure that make up hotspot 6 are coloured by the number of times that they have been affected by a Homologous Recombination event (see key at the top right).
