Eukaryotic organisms constantly face a wide range of internal and external factors that cause damage to their DNA. Failure to accurately and efficiently repair these DNA lesions can result in genomic instability and the development of tumors (Canela et al., 2017). Among the various forms of DNA damage, DNA double-strand breaks (DSBs) are particularly harmful. Two major pathways, non-homologous end joining (NHEJ) and homologous recombination (HR), are primarily responsible for repairing DSBs (Katsuki et al., 2020; Li and Yuan, 2021; Zhang and Gong, 2021; Xiang et al., 2023). NHEJ is an error-prone repair mechanism that simply joins the broken ends together (Blunt et al., 1995; Hartley et al., 1995). In contrast, HR is a precise repair process. It involves multiple proteins in eukaryotic cells, with the RAD51 recombinase being the key player, which is analogous to bacterial recombinase A (RecA) (Shinohara et al., 1992). The central event in HR is the formation of RAD51-single-stranded DNA (ssDNA) nucleoprotein filaments that facilitate homology search and DNA strand invasion, ultimately leading to the initiation of repair synthesis (Miné et al., 2007; Hilario et al., 2009; Ma et al., 2017).
Recombinational DNA Repair ; DNA-Binding Proteins/metabolism* ; DNA Repair ; DNA Damage ; DNA

The present study was carried out to find a simple and safe in. vitro test for phtotoxic drugs. Authors selected two strains of Salmonella typhimurium(TA98 and TA102) which have been used in Ames test for the detsction of mutagenecity af various chemical substances. Both strains are genuine products of genetic enzineering. The etrain TA98 should be highly vulnerable to ultraviolet radition because it lacks normal I)NA excision repair gene. The strain TA102 was chosen as control since it maintained the DNA repair gene. These strains were subjected to increasing dosea of UVA with or without pretreatment of 8 methoxypsoralsn(8-MOP) which is a prototype of photatoxic druge. The authors made use of a perforated stain-less steel template which provided a simple and eosy monitoring of ultraviolet irradiation effects i.e. clear zones due to inhibition of the atrains could be determined. By using this methad, the authors acquired the following results .' I. 8-MOP alone exerted no inhibition on both strains at concentration upto 100mg /ml. 2. UVA irradiation alone showed no growth inhibition at dose upto 5J/cm. 3. UVA irradiation after pretreatment with 8 MOP resulted varying growth inhibition in proportion to irradiation doses. 4. Authors found a suitable concentration of 8-MOP for this test is 10pg/ml. With this ccncentrstion, minimal phatatoxic dose of UVA were O.l J/cm for the strain TA98 and 1.0J/cm for the strain TA102 respectively.
Dermatitis, Phototoxic ; DNA Repair ; Methoxsalen ; Salmonella ; Steel

Animals ; DNA Damage ; DNA Repair ; DNA-Activated Protein Kinase ; Humans

Animals ; DNA Damage ; DNA Repair ; DNA, Neoplasm ; Humans

DNA ; DNA Damage ; DNA Repair ; Fanconi Anemia/genetics* ; Humans

53BP1 is an important genome stability regulator, which protects cells against double-strand breaks. Following DNA damage, 53BP1 is rapidly recruited to sites of DNA breakage, along with other DNA damage response proteins, including gamma-H2AX, MDC1, and BRCA1. The recruitment of 53BP1 requires a tandem Tudor fold which associates with methylated histones H3 and H4. It has already been determined that the majority of DNA damage response proteins are phosphorylated by ATM and/or ATR after DNA damage, and then recruited to the break sites. 53BP1 is also phosphorylated at several sites, like other proteins after DNA damage, but this phosphorylation is not critically relevant to recruitment or repair processes. In this study, we evaluated the functions of phosphor-53BP1 and the role of the BRCT domain of 53BP1 in DNA repair. From our data, we were able to detect differences in the phosphorylation patterns in Ser25 and Ser1778 of 53BP1 after neocarzinostatin-induced DNA damage. Furthermore, the foci formation patterns in both phosphorylation sites of 53BP1 also evidenced sizeable differences following DNA damage. From our results, we concluded that each phosphoryaltion site of 53BP1 performs different roles, and Ser1778 is more important than Ser25 in the process of DNA repair.
DNA ; DNA Damage ; DNA Repair ; Genomic Instability ; Histones ; Phosphorylation ; Proteins

Cell Line, Tumor ; DNA Repair ; DNA Repair Enzymes ; Hep G2 Cells ; Humans

Clustered regulatory interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 nuclease (Cas9), the third-generation genome editing tool, has been favored because of its high efficiency and clear system composition. In this technology, the introduced double-strand breaks (DSBs) are mainly repaired by non-homologous end joining (NHEJ) or homology-directed repair (HDR) pathways. The high-fidelity HDR pathway is used for genome modification, which can introduce artificially controllable insertions, deletions, or substitutions carried by the donor templates. Although high-level knock-out can be easily achieved by NHEJ, accurate HDR-mediated knock-in remains a technical challenge. In most circumstances, although both alleles are broken by endonucleases, only one can be repaired by HDR, and the other one is usually recombined by NHEJ. For gene function studies or disease model establishment, biallelic editing to generate homozygous cell lines and homozygotes is needed to ensure consistent phenotypes. Thus, there is an urgent need for an efficient biallelic editing system. Here, we developed three pairs of integrated selection systems, where each of the two selection cassettes contained one drug-screening gene and one fluorescent marker. Flanked by homologous arms containing the mutated sequences, the selection cassettes were integrated into the target site, mediated by CRISPR/Cas9-induced HDR. Positively targeted cell clones were massively enriched by fluorescent microscopy after screening for drug resistance. We tested this novel method on the amyloid precursor protein (APP) and presenilin 1 (PSEN1) loci and demonstrated up to 82.0% biallelic editing efficiency after optimization. Our results indicate that this strategy can provide a new efficient approach for biallelic editing and lay a foundation for establishment of an easier and more efficient disease model.
Alleles ; CRISPR-Cas Systems ; DNA End-Joining Repair ; Gene Editing/methods* ; Recombinational DNA Repair

Consensus ; DNA Repair ; Humans ; Male ; Prostatic Neoplasms/genetics* ; Recombinational DNA Repair

No abstract available
DNA Repair* ; DNA* ; Endonucleases* ; Skin Neoplasms* ; Skin* ; Xeroderma Pigmentosum