We developed a method for genome-wide mapping of DNA excision repair named XR-seq (excision repair sequencing). Human nucleotide excision repair generates two incisions surrounding the site of damage, creating an ∼30-mer. In XR-seq, this fragment is isolated and subjected to high-throughput sequencing. We used XR-seq to produce stranded, nucleotide-resolution maps of repair of two UV-induced DNA damages in human cells: cyclobutane pyrimidine dimers (CPDs) and (6-4) pyrimidine-pyrimidone photoproducts [(6-4)PPs]. In wild-type cells, CPD repair was highly associated with transcription, specifically with the template strand. Experiments in cells defective in either transcription-coupled excision repair or general excision repair isolated the contribution of each pathway to the overall repair pattern and showed that transcription-coupled repair of both photoproducts occurs exclusively on the template strand. XR-seq maps capture transcription-coupled repair at sites of divergent gene promoters and bidirectional enhancer RNA (eRNA) production at enhancers. XR-seq data also uncovered the repair characteristics and novel sequence preferences of CPDs and (6-4)PPs. XR-seq and the resulting repair maps will facilitate studies of the effects of genomic location, chromatin context, transcription, and replication on DNA repair in human cells.

Formation and repair of UV-induced DNA damage in human cells are affected by cellular context. To study factors influencing damage formation and repair genome-wide, we developed a highly sensitive single-nucleotide resolution damage mapping method [high-sensitivity damage sequencing (HS-Damage-seq)]. Damage maps of both cyclobutane pyrimidine dimers (CPDs) and pyrimidine-pyrimidone (6-4) photoproducts [(6-4)PPs] from UV-irradiated cellular and naked DNA revealed that the effect of transcription factor binding on bulky adducts formation varies, depending on the specific transcription factor, damage type, and strand. We also generated time-resolved UV damage maps of both CPDs and (6-4)PPs by HS-Damage-seq and compared them to the complementary repair maps of the human genome obtained by excision repair sequencing to gain insight into factors that affect UV-induced DNA damage and repair and ultimately UV carcinogenesis. The combination of the two methods revealed that, whereas UV-induced damage is virtually uniform throughout the genome, repair is affected by chromatin states, transcription, and transcription factor binding, in a manner that depends on the type of DNA damage.

We recently developed a high-resolution genome-wide assay for mapping DNA excision repair named eXcision Repair-sequencing (XR-seq) and have now used XR-seq to determine which regions of the genome are subject to repair very soon after UV exposure and which regions are repaired later. Over a time course, we measured repair of the UV-induced damage of cyclobutane pyrimidine dimers (CPDs) (at 1, 4, 8, 16, 24, and 48 h) and (6-4)pyrimidinepyrimidone photoproducts [(6-4)PPs] (at 5 and 20 min and 1, 2, and 4 h) in normal human skin fibroblasts. Each type of damage has distinct repair kinetics. The (6-4)PPs are detected as early as 5 min after UV treatment, with the bulk of repair completed by 4 h. Repair of CPDs, which we previously showed is intimately coupled to transcription, is slower and in certain regions persists even 2 d after UV irradiation. We compared our results to the Encyclopedia of DNA Elements data regarding histone modifications, chromatin state, and transcription. For both damage types, and for both transcription-coupled and general excision repair, the earliest repair occurred preferentially in active and open chromatin states. Conversely, repair in regions classified as "heterochromatic" and "repressed" was relatively low at early time points, with repair persisting into the late time points. Damage that remains during DNA replication increases the risk for mutagenesis. Indeed, laterepaired regions are associated with a higher level of cancer-linked mutations. In summary, we show that XR-seq is a powerful approach for studying relationships among chromatin state, DNA repair, genome stability, mutagenesis, and carcinogenesis.DNA repair | DNA damage | chromatin | transcription | mutation D NA damage blocks transcription and replication and compromises the integrity of the genome. Bulky adducts in DNA, the focus of this work, are caused by a variety of genotoxic agents including UV radiation in sunlight. In human cells, this damage is removed exclusively by the nucleotide excision repair mechanism (1-3). In nucleotide excision repair, a single-stranded oligomer that contains the bulky adduct is excised by dual incisions bracketing the lesion. The resulting gap is filled in by DNA polymerases, and the newly synthesized repair patch is then sealed by DNA ligase. In general excision repair, damage recognition is achieved by the repair factors xeroderma pigmentosum (XP) complementation group C (XPC) together with replication protein A (RPA) and XPA (4-6). In DNA that is being actively transcribed, damage recognition can also be achieved by a stalled RNA polymerase II, which, with the aid of the Cockayne Syndrome B (CSB) protein, accelerates the recruitment of the excision repair factors. This recognition process leads to transcription-coupled repair (7,8). The subsequent dual-incision reaction is carried out by the core excision repair factors RPA, XPA, transcription factor II H (TFIIH), XPG, and XPF-ERCC1, releasing an excised oligomer that is 24-32 nucleotides (nt) in length (6, 9).The mechanism of DNA...

Cisplatin is a major anticancer drug that kills cancer cells by damaging their DNA. Cancer cells cope with the drug by removal of the damages with nucleotide excision repair. We have developed methods to measure cisplatin adduct formation and its repair at single-nucleotide resolution. "Damage-seq" relies on the replication-blocking properties of the bulky base lesions to precisely map their location. "XR-seq" independently maps the removal of these damages by capturing and sequencing the excised oligomer released during repair. The damage and repair maps we generated reveal that damage distribution is essentially uniform and is dictated mostly by the underlying sequence. In contrast, cisplatin repair is heterogeneous in the genome and is affected by multiple factors including transcription and chromatin states. Thus, the overall effect of damages in the genome is primarily driven not by damage formation but by the repair efficiency. The combination of the Damageseq and XR-seq methods has the potential for developing novel cancer therapeutic strategies.] is a major frontline drug in the treatment of lung, colorectal, ovarian, and head-and-neck cancers (1) and has been used in the clinic since 1978. It kills cancer cells by damaging their DNA, mainly by forming Pt-d(GpG) and, to a lesser extent, Pt-d(ApG), Pt-d(GpXpG) intrastrand diadduct, and at lower frequency, Pt-G-G interstrand cross-links (2-4). The cisplatin-induced damage is repaired by nucleotide excision repair (5-8). In excision repair, the damage in DNA is excised from the genome as a single-stranded oligomer of ∼30 nt. The single-stranded gap in the genome is filled in by DNA polymerases and ligated, resulting in error-free repair. Although cisplatin is effective in the treatment of the indicated types of cancers, in some of the cases, drug resistance is observed. The cause of the resistance is multifactorial, and DNA repair is considered to be one of the contributing factors, although the degree to which DNA repair contributes to resistance is still unclear. Here, we describe the development of methods to measure cisplatin adduct formation and repair at single-nucleotide resolution. Using these methods, named "Damage-seq" and "eXcision Repairseq" (XR-seq), we have generated single-nucleotide resolution maps for both the damage induced by cisplatin and its removal by nucleotide excision repair (9, 10). Our method should be applicable for studying drug resistance and for optimization of cancer chemotherapy regimens. ResultsIn this work, we present the cisplatin damage and repair maps for the entire genome of the human lymphocyte cell line GM12878. This cell line was chosen because it has been extensively characterized by the ENCODE project (11). Similar experiments with oxaliplatin, a third generation derivative of cisplatin, yielded similar results and are presented in SI Appendix, SI Materials and Methods. All experiments were performed with two biological replicates.Cisplatin DNA Damage Map. We developed the method of Damage-seq based on the fact th...

DNA replication across blocking lesions occurs by translesion DNA synthesis (TLS), involving a multitude of mutagenic DNA polymerases that operate to protect the mammalian genome. Using a quantitative TLS assay, we identified three main classes of TLS in human cells: two rapid and error-free, and the third slow and error-prone. A single gene, REV3L, encoding the catalytic subunit of DNA polymerase f (polf), was found to have a pivotal role in TLS, being involved in TLS across all lesions examined, except for a TT cyclobutane dimer. Genetic epistasis siRNA analysis indicated that discrete two-polymerase combinations with polf dictate error-prone or error-free TLS across the same lesion. These results highlight the central role of polf in both error-prone and error-free TLS in mammalian cells, and show that bypass of a single lesion may involve at least three different DNA polymerases, operating in different two-polymerase combinations.