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Note for: DNA double-strand break repair in a cellular context (doi: 10.1016/j.clon.2014.02.004) Tumour cells not only gain unlimited proliferative capacity, but the ability to adapt to a constantly changing microenvironment. DDR is modified to serve the cancerous phenotype, and if we understand the reasons behind we can get the right target to against the cancer. Non-homologous end-joining (NHEJ) represents the major DNA double-strand break (DSB) repair pathway in mammalian cells. DNA-PKcs undergoes autophosphorylation at clustered sites. DNA-PKcs undergoes autophosphorylation at clustered sites. End-processing can involve the Artemis nuclease, polynucleotide kinase 3' phosphatase and polymerases, including pol-lamda or pol-mu. Whereas NHEJ has beauty in its simplicity, homologous recombination’s elegance lies in its complexity and its exploitation of an undamaged homologous template to restore any lost sequence information. One such process is alternative NHEJ ...

Note for: Systematic E2 screening reveals a UBE2D-RNF138-CtIP axis promoting DNA repair (doi: 10.1038/ncb3260) Very nice piece of work, I would say. It reflects the complexity of living thing is, especially, post-translational modification processes which control the cellular function through adding the small molecule namely ubiquitin to certain protein. Unrepaired DSB -- genome instability, tumorigenesis, neurodegeneration or premature ageing. The team used UBE2Ds to screen for the binding partner during the DSB responses (using IR in this case). This study found RNF138 was the binding partner for UBE2Ds during the DSB responses. RNF138 promotes CtIF ubiquitination. Key to initiating HR is DNA-end resection promoted by CtIP (RBBP8) recruitment to DSB sites, yielding single-stranded DNA (ssDNA) that is rapidly bound by RPA and subsequently replaced by RAD51, leading to strand invasion and ensuing HR processes. Gap -- how CtIP and early HR events are regulated, ho...

Two papers that I have read; one is the short communication which briefs the major finding of RNF138 contributing to DNA repair. The other paper is the original paper which performed the experiments to show that RNF138 is the new finding regulator of HR. Note for – 1.   RNF138 joins the HR team (doi: 10.1038/ncb3262) 2.   The RNF138 E3 ligase displaces Ku to promote DNA end resection and regulate DNA repair  pathway choice (doi: 10.1038/ncb3259)   RNF138 will be a good target for the choice switching between HR and NHEJ. Protein modification by ubiquitin has a central role in regulating DSB repair. Each cell cycle fate, will be controlled by different sets of protein through the ubiquitination process, like in this case, it is showed that RNF138 promote Ku ubiquitination during S and G2 phase when resection is operational. Cell cycle stage and DNA end resection are believed to regulate the commitment to HR repair. This study identifies RNF138 (Ub-E...

Note: Differential usage of non-homologous end-joining and homologous recombination in double strand break repair (doi: 10.1016/j.dnarep.2006.05.022 ) they mentioned that HR play dominant role in yeast, however, NHEJ contributes to DSB repair in vertebrates (my guess is that higher vertebrate genome is more complex, NHEJ is much easier to solve DSB very quick). There is the tight regulation on the switching HR and NHEJ -- events that determine the cell to go for either HR or NHEJ is cell cycle phase and DSB nature. DSB is lethal damage, if there is one unrepaired DSB, it can induce apoptosis. For the cycling cell, DSB occurs mainly during the replication. For the ionizing radiation -- i can generate break at any stages, or even the "packed chromatin" -- therefore, during the G2 and G1 which the chromosomes are packed -- it will be hard to find the homology in G2 (from sister-chromatid which is "packed") and the homology in G1 (from homology se...

Note: Genetic dissection of vertebrate 53BP1: A major role in non-homologous end joining of DNA double strand breaks (doi: http://dx.doi.org/10.1016/j.dnarep.2006.03.008 ) mutation of 53BP1 in mammalian causing 1.cellular sensitivity toward radiation. 2.defect in checkpoint But DT40-53BP1(-/-) 1.intra-S phase checkpoint was normal 2.G2-M checkpoint was normal once there is the DSB -- 53BP1 is the earliest protein to recruit and form foci. In mammalian, defect in 53BP1 causes the cell cycle delays after the damage. The sequence of NHEJ; 1. Ku70/80 2.DNA-PK --> phosphorylate Artemis nuclease Artemis in IR break fixing is required more studies. Late S-G2; HR and NHEJ play role in "IR-induced" double strand break G1-early S; NHEJ is dominant AA from 203-1716 was removed. Sensitivity toward irradiation with asynchronously growing 53BP1-/- -->biphasic pattern. 53BP1(-/-) also increased the rate of HR --> this mean th...

Note for: Reverse genetic studies of the DNA damage response in the chicken B lymphocyte line DT40 (doi: 10.1016/j.dnarep.2004.03.039) Post-genomic era --> 1. reverse genetic tool is used to study the protein function 2. ppl using DT40 bc of many advantages; - efficient gene targeting - stable phenotype - lack p53 allow us to study the DNA damage due to the cells still can go through the interphase checkpoint even they have the error --  this is the reason why it is a good model to study the DNA damage and repair by observing on the chromosome. In higher eukaryote; 1. human and mouse, B-lymphocyte develop in bone marrow Functional IgV segments generate through site-specific process called V(D)J recombination 2. rabbit and chicken, B-lymphocyte develop in specific tissue; R-appendix of intestinal tract/C-bursa of Fabricius Functional IgV generate through intragenic homologous DNA recombination, called Ig gene conversion. Mature B-lymphocyte; hu...