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Here the authors show that PARP2 drives telomere fragility by orchestrating the Break-induced replication (BIR) pathway. This promotes DNA end resection and DNA synthesis via the regulation of POLD3.

Photolyase is an enzyme responsible for repairing DNA which is damaged after exposure to UV light. Here, the authors use site directed mutagenesis and femtosecond spectroscopy to study how photolyase achieves its maximal repair efficiency.

Incorporation of mismatched nucleotides during DNA replication or repair can lead to mutagenesis. Here the authors reveal that DNA ligase can ligate NHEJ intermediates following incorporation of 8-oxodGTP or dGTP opposite T by DNA Polymerase mu (Pol mu) in vitro, which suggests that Pol mu could cause promutagenic mismatches during DSB repair.

In this study, the authors present structures and functional analyses for the RAD51C-XRCC3 tumor suppressor complex, providing insights into recurrent mutations in cancer and Fanconi Anemia patients that uncover distinct DNA replication fork protection, restart and reversal regions.

CRISPR systems lacking Cas4 can use fused or recruited exonucleases for faithful acquisition of new CRISPR immune sequences.

ASCC3 is a multi-functional helicase that contains two consecutive Ski2-like helicase units. Here, the authors show that ASCC3 can unwind DNA by threading one strand of a substrate duplex through both helicase units, supported by the TRIP4 protein.

AP endonuclease 1 (APE1) processes genomic AP sites during base excision repair. Here, the authors determine the structural mechanism used by APE1 to process nucleosomal AP sites, providing new insight into DNA repair in chromatin.

The repair enzyme (6–4) photolyase uses light energy to cleave the ultraviolet-induced bond between pyrimidine dimers. These authors use ultrafast spectroscopy to examine the detailed electron and proton movements during the catalytic photocycle. Histidine 364 is identified as the crucial residue involved in the rate-limiting step.

5'-adenylated DNA adducts generated during nucleotide excision repair (NER) are removed by aprataxin to permit DNA end ligation. Now, structural and kinetic analyses reveal that NER enzymes DNA polymerase β and FEN1 can also excise these adducts and thus provide a 'backup' repair pathway for abasic sites.

Aprataxin is a DNA deadenylase that processes DNA molecules with 5'-AMP termini that result from abortive ligation reactions. The crystal structures of the Schizosaccharomyces pombe ortholog Hnt3 in its apo state, bound to DNA or DNA and AMP, provide insight into how this enzyme recognizes and processes its substrate.

The ends of chromosomes, known as telomeres, look like ends generated by double-strand breaks, but if treated as such the DNA damage repair system would initiate a checkpoint response and cause telomere–telomere fusions. These authors show that telomeres lack two types of histone modification that are required for recruitment of Crb2^b53BP1, without which the checkpoint cannot be activated even if other DNA damage response proteins are recruited to a Taz1-deficient telomere.

Human Bloom’s syndrome (BLM) helicase has a role in DNA repair, and BLM deficiency in humans is associated with chromosomal abnormalities. Here the authors employ solution biophysical assays to show BLM maintains a balance for disruption and stabilization of oligonucleotide-based D-loops. Interaction with the Topoisomerase IIIalpha-RMI1-RMI2 complex orients the activity toward D-loop disruption.

Microbial DNA glycosylases associated with the biosynthesis of DNA-damaging antibiotics have evolved self-resistance for their cognate natural products. Here, the authors provide evidence that cellular self-resistance is enabled by reduced affinity of the glycosylases for the excision products of the corresponding DNA lesions.

The current model for B-family DNA polymerases in archaea is one of single-subunit enzymes in contrast to the multi-subunit complexes in eukaryotes. Here the authors show that PolB1 fromSulfolobus solfataricusexists as a heterotrimeric complex in cell extracts.

Reusswig et al. use engineered systems to force DNA replication in the G1 phase of the cell cycle. This unscheduled G1 replication shows hallmarks of S phase replication, but leads to over-replication and DNA breaks from replication collisions.

Poly-ADP-ribosylation (PARylation) is a well-known posttranslational modification of proteins. Here the authors show that beyond proteins also mammalian single-stranded DNA is PARylated in vitro and in vivo.

Recent findings revealed that DNA–protein crosslinks (DPCs) in yeast and Xenopus laevis are repaired by a dedicated, protease-based DNA-repair pathway. Mutations in the putative human homologue of a DPC protease result in premature ageing and cancer predisposition.

Repair of double-strand DNA breaks by homologous recombination can be carried out in bacteria by RecBCD, AddAB and AdnAB. Here, Dale Wigley discusses recent insights into how these complexes mediate repair, as well as their evolution.

The PARP2–HPF1 histone-modifying complex bridges two nucleosomes to align broken DNA ends for ligation, initiating conformational changes that activate PARP2 and enable DNA damage repair.

PARP1 is the target of clinically approved anti-cancer drugs whose in vivo efficacy has been hard to predict. Here the authors show how an altered active site formed between PARP1 and Histone PARylation Factor 1 (HPF1) changes the efficacy of some of these inhibitors.

Structures of USP1−UAF complexes, including a cryo-EM structure of USP−UAF1 bound to its substrate FANCI−FANCD2, reveal molecular details of USP1−UAF1 regulation and substrate recognition.

Transcription-repair coupling factors (TRCFs) are large ATPases that mediate the preferential repair of the transcribed DNA strand. Here the authors reveal the cryo-EM structure of DNA-bound Mfd, the bacterial TRCF, and provide molecular insights into its mode of action.

A new cryo-EM structure of human DNA-PKcs in complex with a Ku70/80 heterodimer and DNA reveals how Ku80–DNA-PKcs interactions create a scaffold to mediate DNA double-strand break repair.

New data show that the HMCES protein suppresses DNA double-strand break formation by cross-linking to and thereby stabilizing an abasic site generated during replication-coupled repair of a DNA interstrand cross-link, thus demonstrating a physiological role of HMCES in DNA repair.

The poly(ADP-ribose) polymerases play a key role in maintaining genomic integrity by detecting DNA damage and mediating repair. Here the authors characterize the kinetics of PARP1 binding to a variety of nucleosomes harbouring DNA double-strand breaks.

In Escherichia coli, the UvrAB damage sensor recognizes helix-distorting lesions by itself or via Mfd bound to stalled RNA polymerase. Here authors use single-molecule fluorescence imaging to quantify the kinetic signatures of interactions of UvrA with Mfd and UvrB in live cells.

PALB2 is an established breast cancer risk gene but the pathogenicity of many variants remains uncharacterised. Here, the authors present a cDNA-based system for the functional analysis of PALB2 variants of unknown significance.

DNA polymerase θ is a polymerase-helicase essential for microhomology-mediated end-joining (MMEJ) or alternative end-joining of DNA. Here the authors use biochemical and biophysical methods to reveal how full-length human DNA polymerase θ performs MMEJ at the molecular level.

Mfd recognizes stalled transcriptional complexes at sites of lesions and recruits the nucleotide excision repair proteins (UvrAB) to the site. Here the authors use live cell imaging in E. coli to demonstrate that coordinated ATP hydrolysis by UvrA and loading of UvrB on DNA facilitate the dissociation of Mfd from the handoff complex.

Post-translational modifications are critical for regulating the DNA damage response. Here, the authors identify a methylation-deubiquitination crosstalk between methyltransferase PRMT1 and deubiquitinase USP11, showing that the enzymes regulate each other’s functions in DNA repair.

CAPPs are putative Primase-Polymerases associated with CRISPR-Cas operons. Here, the authors show CAPPs genetic and physical association with Cas1 and Cas2, their capacity to function as DNA-dependent DNA primases and DNA polymerases, and that Cas1-Cas2 complex adjacent to CAPP has bona fide spacer integration activity.

Structural and mechanistic data of the ADP-ribosyltransferase DarT demonstrate the role of ADP-ribosylation of DNA by this enzyme in generating toxicity and regulating cellular signalling processes in bacteria.

The high expression of the DNA repair enzyme O6-methylguanine DNA methyltransferase (MGMT) often confers resistance to chemotherapy in several cancers. In this study, the authors propose the inhibition of the Wnt signalling pathway as an alternative strategy to modulate MGMT expression and sensitize tumours to chemotherapy.

Oxidative stress is a common source of DNA damage and is repaired by the base excision repair machinery, including polymerase beta. Here the authors find that polymerase beta, and to a lesser extent lambda, can mistakenly incorporate ribonucleotides during synthesis.

Several mechanisms are in place to ensure the accurate and timely replication of the genome as cells progress through S-phase. Here, the authors show that Mus81, an endonuclease involved in the response to DNA damage during replicative stress, also regulates the rate of DNA replication during normal growth.

Uridines at the wobble position of transfer RNA anticodons are usually modified to allow efficient decoding of messenger RNA codons. In this study, ALKBH8 is shown to be a bifunctional transfer RNA modification enzyme required for the formation of a novel diastereomeric pair of modified wobble uridines.

Chromatin regulators facilitate repair of DNA double-strand breaks in chromosomal DNA. The authors show that the recruitment of such chromatin regulators to DNA lesions is controlled by the choice of DNA repair pathway.

WABS patient derived cells display loss of sister chromatid cohesion. Here the authors by analyzing WABS patient derived cells, reveal a role of the DDX11 helicase in resolving G-Quadruplex structures to support sister chromatid cohesion.

A combination of biochemical, single-molecule, and in vivo assays reveals that the UV-DDB complex that removes UV-induced DNA lesions via the nucleotide excision repair pathway also promotes removal of oxidative lesions via base excision repair.

Clairmont et al. find that the TRIP13 ATPase regulates REV7–Shieldin dissociation to promote homology-directed repair and suppress non-homologous end joining, and show the importance of PARPi resistance in BRCA1-deficient cancers.

Homologous recombination requires end resection of the DNA at the site of the break, however the Ku dimer can sequester single-ended double-strand breaks. Here the authors show that ATM-dependent phosphorylation of CtIP, along with the actions of Mre11, impair the stable loading of Ku onto DNA.

The E3 ligase RNF168 is essential for the signalling of DNA double strand break and its mutations are associated with the RIDDLE syndrome. Here the authors identify TOP2a as substrate for RNF168 and USP10; providing a link between the RNF168/USP10 axis, TOP2a and the response to anti-cancer drugs that target TOP2.

Crystal structures of the Ku70/80–DNA complex with Ku binding motifs of APLF and XLF reveal distinct interaction sites and an induced conformational change in Ku80 critical for function in NHEJ repair.

RecN is a cohesin-like molecule involved in the bacterial response to DNA double-strand breaks. Here the authors provide evidence that RecN stimulates the DNA strand invasion step of RecA-mediated recombination.

Chromosomal single-strand DNA breaks occur frequently and require repair to avoid disease outcomes. Here, the authors show that in bird cells, PARP3 accelerates this repair, and use structural biology and cell biology techniques to reveal details of the mechanism of action.

DNA-repair enzyme Tdp2 hydrolyzes the 5'-phosphotyrosine bond formed by topoisomerases and is associated with resistance to anticancer drugs that trap such complexes. The crystal structures of zebrafish Tdp2 bound to DNA offer insight into substrate recognition. In addition, the crystal structure of nematode Tdp2 suggests a potential mechanism for autoregulation.

Dysfunctional redox regulation in cancer can damage dNTPs so inhibiting dNTP pool sanitizing enzymes, such as MTH1, is a potential cancer treatment. Here, Carter et al.characterize MTH2 (NUDT15) and show that it is not a dNTP sanitizer, and so is unlikely to influence the efficacy of MTH1 inhibitors.