scholarly journals Multiple Pathways for Repair of DNA Double-Strand Breaks in Mammalian Chromosomes

1999 ◽  
Vol 19 (12) ◽  
pp. 8353-8360 ◽  
Author(s):  
Yunfu Lin ◽  
Tamas Lukacsovich ◽  
Alan S. Waldman
Keyword(s):  
Homologous Recombination ◽  
Double Strand Breaks ◽  
Nonhomologous End Joining ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Base Pairs ◽  
Dsb Repair ◽  
Strand Breaks ◽  
Single Strand Annealing ◽  
Strand Annealing

ABSTRACT To study repair of DNA double-strand breaks (DSBs) in mammalian chromosomes, we designed DNA substrates containing a thymidine kinase (TK) gene disrupted by the 18-bp recognition site for yeast endonuclease I-SceI. Some substrates also contained a second defective TK gene sequence to serve as a genetic donor in recombinational repair. A genomic DSB was induced by introducing endonuclease I-SceI into cells containing a stably integrated DNA substrate. DSB repair was monitored by selection for TK-positive segregants. We observed that intrachromosomal DSB repair is accomplished with nearly equal efficiencies in either the presence or absence of a homologous donor sequence. DSB repair is achieved by nonhomologous end-joining or homologous recombination, but rarely by nonconservative single-strand annealing. Repair of a chromosomal DSB by homologous recombination occurs mainly by gene conversion and appears to require a donor sequence greater than a few hundred base pairs in length. Nonhomologous end-joining events typically involve loss of very few nucleotides, and some events are associated with gene amplification at the repaired locus. Additional studies revealed that precise religation of DNA ends with no other concomitant sequence alteration is a viable mode for repair of DSBs in a mammalian genome.

scholarly journals Rejoining of DNA Double-Strand Breaks as a Function of Overhang Length

2005 ◽  
Vol 25 (3) ◽  
pp. 896-906 ◽  
Author(s):  
James M. Daley ◽  
Thomas E. Wilson
Keyword(s):  
Gc Content ◽  
Double Strand Breaks ◽  
Nonhomologous End Joining ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Strand Breaks ◽  
Single Strand Annealing ◽  
Primary Determinant ◽  
Overhang Length ◽  
Strand Annealing

ABSTRACT The ends of spontaneously occurring double-strand breaks (DSBs) may contain various lengths of single-stranded DNA, blocking lesions, and gaps and flaps generated by end annealing. To investigate the processing of such structures, we developed an assay in which annealed oligonucleotides are ligated onto the ends of a linearized plasmid which is then transformed into Saccharomyces cerevisiae. Reconstitution of a marker occurs only when the oligonucleotides are incorporated and repair is in frame, permitting rapid analysis of complex DSB ends. Here, we created DSBs with compatible overhangs of various lengths and asked which pathways are required for their precise repair. Three mechanisms of rejoining were observed, regardless of overhang polarity: nonhomologous end joining (NHEJ), a Rad52-dependent single-strand annealing-like pathway, and a third mechanism independent of the first two mechanisms. DSBs with overhangs of less than 4 bases were mainly repaired by NHEJ. Repair became less dependent on NHEJ when the overhangs were longer or had a higher GC content. Repair of overhangs greater than 8 nucleotides was as much as 150-fold more efficient, impaired 10-fold by rad52 mutation, and highly accurate. Reducing the microhomology extent between long overhangs reduced their repair dramatically, to less than NHEJ of comparable short overhangs. These data support a model in which annealing energy is a primary determinant of the rejoining efficiency and mechanism.

scholarly journals Human RNF169 is a negative regulator of the ubiquitin-dependent response to DNA double-strand breaks

2012 ◽  
Vol 197 (2) ◽  
pp. 189-199 ◽  
Author(s):  
Maria Poulsen ◽  
Claudia Lukas ◽  
Jiri Lukas ◽  
Simon Bekker-Jensen ◽  
Niels Mailand
Keyword(s):  
Deoxyribonucleic Acid ◽  
Double Strand Breaks ◽  
Negative Regulator ◽  
Nonhomologous End Joining ◽  
Genome Integrity ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Dsb Repair ◽  
Strand Breaks ◽  
Protein Recruitment

Nonproteolytic ubiquitylation of chromatin surrounding deoxyribonucleic acid double-strand breaks (DSBs), mediated by the RNF8/RNF168 ubiquitin ligases, plays a key role in recruiting repair factors, including 53BP1 and BRCA1, to reestablish genome integrity. In this paper, we show that human RNF169, an uncharacterized E3 ubiquitin ligase paralogous to RNF168, accumulated in DSB repair foci through recognition of RNF168-catalyzed ubiquitylation products by its motif interacting with ubiquitin domain. Unexpectedly, RNF169 was dispensable for chromatin ubiquitylation and ubiquitin-dependent accumulation of repair factors at DSB sites. Instead, RNF169 functionally competed with 53BP1 and RAP80–BRCA1 for association with RNF168-modified chromatin independent of its catalytic activity, limiting the magnitude of their recruitment to DSB sites. By delaying accumulation of 53BP1 and RAP80 at damaged chromatin, RNF169 stimulated homologous recombination and restrained nonhomologous end joining, affecting cell survival after DSB infliction. Our results show that RNF169 functions in a noncanonical fashion to harness RNF168-mediated protein recruitment to DSB-containing chromatin, thereby contributing to regulation of DSB repair pathway utilization.

scholarly journals Different Roles for Nonhomologous End Joining and Homologous Recombination following Replication Arrest in Mammalian Cells

2002 ◽  
Vol 22 (16) ◽  
pp. 5869-5878 ◽  
Author(s):  
Cecilia Lundin ◽  
Klaus Erixon ◽  
Catherine Arnaudeau ◽  
Niklas Schultz ◽  
Dag Jenssen ◽  
...  
Keyword(s):  
Homologous Recombination ◽  
Mammalian Cells ◽  
Double Strand Breaks ◽  
Nonhomologous End Joining ◽  
Replication Forks ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Lethal Effects ◽  
Strand Breaks ◽  
Replication Arrest

ABSTRACT Homologous recombination (HR) and nonhomologous end joining (NHEJ) play overlapping roles in repair of DNA double-strand breaks (DSBs) generated during the S phase of the cell cycle. Here, we characterized the involvement of HR and NHEJ in the rescue of DNA replication forks arrested or slowed by treatment of hamster cells with hydroxyurea or thymidine. We show that the arrest of replication with hydroxyurea generates DNA fragmentation as a consequence of the formation of DSBs at newly replicated DNA. Both HR and NHEJ protected cells from the lethal effects of hydroxyurea, and this agent also increased the frequency of recombination mediated by both homologous and nonhomologous exchanges. Thymidine induced a less stringent arrest of replication and did not generate detectable DSBs. HR alone rescued cells from the lethal effects of thymidine. Furthermore, thymidine increased the frequency of DNA exchange mediated solely by HR in the absence of detectable DSBs. Our data suggest that both NHEJ and HR are involved in repair of arrested replication forks that include a DSB, while HR alone is required for the repair of slowed replication forks in the absence of detectable DSBs.

scholarly journals Necessities in the Processing of DNA Double Strand Breaks and Their Effects on Genomic Instability and Cancer

Cancers ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1671 ◽  
Author(s):  
George Iliakis ◽  
Emil Mladenov ◽  
Veronika Mladenova
Keyword(s):  
High Speed ◽  
Double Strand Breaks ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Strand Breaks ◽  
Large Deletions ◽  
Single Strand Annealing ◽  
Modes Of Processing ◽  
Non Homologous End Joining ◽  
Strand Annealing

Double strand breaks (DSBs) are induced in the DNA following exposure of cells to ionizing radiation (IR) and are highly consequential for genome integrity, requiring highly specialized modes of processing. Erroneous processing of DSBs is a cause of cell death or its transformation to a cancer cell. Four mechanistically distinct pathways have evolved in cells of higher eukaryotes to process DSBs, providing thus multiple options for the damaged cells. The homologous recombination repair (HRR) dependent subway of gene conversion (GC) removes IR-induced DSBs from the genome in an error-free manner. Classical non-homologous end joining (c-NHEJ) removes DSBs with very high speed but is unable to restore the sequence at the generated junction and can catalyze the formation of translocations. Alternative end-joining (alt-EJ) operates on similar principles as c-NHEJ but is slower and more error-prone regarding both sequence preservation and translocation formation. Finally, single strand annealing (SSA) is associated with large deletions and may also form translocations. Thus, the four pathways available for the processing of DSBs are not alternative options producing equivalent outcomes. We discuss the rationale for the evolution of pathways with such divergent properties and fidelities and outline the logic and necessities that govern their engagement. We reason that cells are not free to choose one specific pathway for the processing of a DSB but rather that they engage a pathway by applying the logic of highest fidelity selection, adapted to necessities imposed by the character of the DSB being processed. We introduce DSB clusters as a particularly consequential form of chromatin breakage and review findings suggesting that this form of damage underpins the increased efficacy of high linear energy transfer (LET) radiation modalities. The concepts developed have implications for the protection of humans from radon-induced cancer, as well as the treatment of cancer with radiations of high LET.

scholarly journals A game of musical chairs: Pro- and anti-resection factors compete for TOPBP1 binding after DNA damage

2017 ◽  
Vol 216 (3) ◽  
pp. 535-537 ◽  
Author(s):  
Kenji Shimada ◽  
Susan M. Gasser
Keyword(s):  
Dna Damage ◽  
Homologous Recombination ◽  
Binding Sites ◽  
Double Strand Breaks ◽  
Nonhomologous End Joining ◽  
Repair Pathway ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Strand Breaks ◽  
Pathway Regulation

DNA double strand breaks (DSBs) are generally repaired through nonhomologous end joining or homologous recombination. In this issue, Liu et al. (2017. J. Cell Biol. https://doi.org/10.1083/jcb.201607031) report that the conserved scaffold protein TOPBP1Dpb11 provides binding sites for both pro- and anti-resection factors at DSBs, providing insights into repair pathway regulation.

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