DNA Repair

53BP1 (p53 binding protein 1) was originally thought to be a p53 transcriptional enhancing partner, but now has been shown to be an ataxia telangiectasia mutated (ATM) substrate. It is a late DNA damage response (DDR) marker, appearing in the telophase/cytokinesis phase in mitotic mammalian cells (1).

NBS1 (Nijmegen breakage syndrome protein 1) is a component of the MRN complex (Mre11-Rad50-Nbs1) that plays important role in detecting DNA double strand breaks (DSBs) and triggering the downstream cascade. DSBs can be caused by ionizing radiation, chemotherapy drugs, metabolic ROS, replication errors, programmed enzymatic activities during meiosis/V(D)J recombination, etc.

An AP (apurinic/apyrimidinic) site, also known as an abasic site, is a region of DNA that is lacking a purine or pyrimidine base. This can occur spontaneously, or as a result of DNA damage. When DNA damage occurs, DNA repair pathways are activated.

8-hydroxyguanine is a form of oxidative DNA damage where free radicals cause G:C to T:A transversions within the backbone. In E. coli, three DNA repair enzymes exist to prevent the mutagenic effects of 8-hydroxyguanine mutations. One of these enzymes, Ogg1, was found to have both functional yeast (yOgg1) and human (hOgg1) homologues. These hOgg1 proteins efficiently release the 8-hydroxyguanine through cleavage.

Ku70, known by several synonyms including X-ray repair cross-complementing, 5'-deoxyribose-5-phosphate lyase Ku70 protein 6, 70 kDa subunit of Ku antigen, XRCC6, and G22P1, is a 70 kDa protein that was shown to be involved in multiple cellular pathways, mainly involving DNA repair and recombination (2).

Bromodeoxyuridine (BrdU) variously abbreviated as BrdU, BudR, and BrdUrd, is a synthetic thymidine analog that gets incorporated into the DNA of dividing cells during the S-phase of the cell cycle and has a long history of heavy use in molecular and cytokinetic studies (1).

RAD51 is a recombinase protein encoded by RAD51 gene in humans. Human RAD51 family members are highly similar to bacterial RecA and yeast Rad51, both biochemically and structurally. It is a 339-amino acid protein that plays an important role in homologous recombination (HR) of DNA during double-strand break (DSB) repair.

APE1 (aka. HAP1, /Ref-1 or APEX) the mammalian ortholog of Escherichia coli Xth is a multifunctional protein possessing both DNA repair and transcriptional regulatory activity. APE1 acts essentially as master regulator of controlling cellular response to oxidative stress, and contributes to the genome stability (1).

The thymidine analogue bromodeoxyuridine (BrdU) has a long, colorful history of heavy use in molecular and cytokinetic studies (1, 2). BrDU is incorporated into newly synthesized DNA only in S-phase cells, and then immunocytochemically detected with BrDU antibodies. This method allows for extremely accurate and comprehensive comparative studies of a variety of cells ranging from normal to neoplastic.

Proliferating Cell Nuclear Antigen (PCNA), also known as the polymerase delta auxiliary protein, is a nuclear protein essential for DNA replication as well as DNA excision and mismatch repair pathways. It has a large role in cell cycle regulation and response of cells to stress.