Proteins involvement in DNA repair

Humans also display marked interindividual variability in the capacity to repair damaged DNA. This variation is partly due to genetic factors, and genetic polymorphisms have been found in several proteins involved in DNA repair (Kalberlah and Schneider 1998, KEMI 2003). 

Nucleotide-excision repair involves PCNA, DNA polymerase epsilon, and several accessory proteins, such as RF-C (replication factor C), RP-A (replication protein A), and Lig I (DNA ligase I). It could be that these proteins form an aggregate DNA repair machine. PCNA is a hollow circular protein that encircles DNA. PCNA binds and activates many proteins involved in DNA repair. Mismatch repair is less well characterized, but involves DNA polymerase delta. 

CAM5.2 and c-kit has been found in 40% of cases of spermatocytic seminoma. Chk2, a regulatory protein in the transition of gonocytes to spermatogonia and from a mitotic phenotype to a meiotic one, and MAGE-A4 (a protein involved in DNA repair) have been found to be positive in more than 90% and 100% of SSs, respec-... 

A large number of proteins involved in DNA repair, recombination and replication have been shown to be induced when required (18-20). The SOS response in E. coli, which coordinates the expression of over twenty genes, is probably the best understood model system demonstrating the functional orientation of transcriptionally induced genes (21). This response to... 

More recently, new methods have been applied to visualize directly the localized damage induced by particle radiation. These methods are based on Immunofluo-rescent staining of nuclear sites containing proteins involved in DNA repair. Accumulation of these proteins is thought to be an indicator of particular severe and probably irreparable damage [86,87]. 

The invariant SQ motif in the C-terminus of H2AX is a consensus sequence for the 3 kinases belonging to the PIKK family, namely ATM, DNA-PK and ATR (Stiff et al, 2004). These kinases are involved in DNA repair. ATM [ataxia telangiectasia (A-T) mutated protein] is a crucial kinase for the signal transduction DSB pathway (Savitsky et al, 1995) and it is widely accepted that ATM is the major kinase involved in the in vivo phosphorylation of H2AX (Burma et al, 2001 Fernandez-Capetillo et al, 2002 Redon et al, 2002). The two other kinases were also associated with the generation y-H2AX, but they appeared not to be dominant (Redon et al, 2002 Stiff et al, 2004). 

A second group of inherited colon cancers are termed hereditary nonpolyposis colorectal cancer (HNPCC). HNPCC may account for 5% of all colon cancer cases and can be caused by mutations in any of five different genes. All of these genes encode proteins involved in DNA mismatch repair (Fig II-5-3). As with inherited breast cancer, fiiulty DNA repair leads to mutated cells capable of producing tumors. 

NaF was not mutagenic in bacterial assays. Although fluoride has been shown to be clas-togenic in a variety of cell types, the mechanism of clastogenicity has been attributed to the effect of fluoride on the synthesis of proteins involved in DNA synthesis and/or repair, rather than direct interaction between fluoride and DNA. In general, there was no effect on sperm morphology or the frequency of chromosomal aberrations, micronuclei, sister chromatid exchange, or DNA strand breaks in rodents treated in vivo. ... 

Mutation is a rare event as far as an individual human being is concerned the probability that a mutation will occur in any one protein is about l in 109. For a human cell it is probably 1 in 105 (calculated from the incidence of haemophilia), but mutagenic agents in effect increase the mutation frequency. Furthermore, a specific mutation in the enzymes involved in DNA repair will also increase the level of mutation. 

The involvement of DNA repair pathways in the development of drug resistance has become increasingly apparent over recent years from in vitro studies on tumor cell lines. Measurement of the expression of specific genes involved in DNA repair pathways in tumor samples has been used to assess the possible clinical significance of DNA repair. Elevated levels of p53 protein in tumors suggest mutation in the p53 gene. As p53 protein is involved in regulation of... 

Double-strand breaks, nicks, and similar DNA damage activate PARP. Once the damage is recognized by PARP, there is a rapid, activation of PARP that quickly activates several enzymes involved in DNA repair. PARP activates transcription factors that regulate the transcription of proteins that may be involved in DNA repair. 

PARP is a nuclear enzyme involved in DNA repair that is activated in response to DNA damage (27). Early during apoptosis, PARP is cleaved by caspases, primarily by caspase-3 (25). The specific cleavage of this protein that results in distinct 89-kDa and 24-kDa fragments (usually detected electrophoretically) is considered one of the hallmarks of apoptosis. Antibodies that recognize the cleaved PARP products were recently developed and they can be used as immunocytochemical markers of apoptotic cells. The antibody to p89 PARP has been adapted to label apoptotic cells for detection by cytometry (28). The protocol below combines the detection of PARP cleavage and cellular DNA content measurement, which allows one not only to identify and score apoptotic cell populations, but also to correlate apoptosis with the cell cycle position or DNA ploidy. 

Eukaryotic DNA polymerases have also been isolated and characterized as listed in Table 22.1. Based on studies of SV40 DNA replication in vitro, it has been found that DNA polymerase d has high processivity and is required for leading-strand synthesis, making it analogous to E. coli DNA pol III. DNA polymerase d requires ATP and is stimulated by two additional DNA replication proteins, RF-C and PCNA. DNA polymerase a serves the same role as E. coli DNA pol I in that DNA polymerase a is necessary for lagging-strand synthesis. In addition to DNA polymerase a and d, three other DNA polymerizing activities have been identified. DNA polymerase I is involved in DNA repair and is most similar to E. coli DNA pol II. DNA polymerase b is also a repair enzyme, and DNA polymerase g is required for mitochondrial DNA synthesis. 

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