Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.99.3 (PRE)
 1,923 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

UV-induced thymine dimers (10 J/m2 of UV-C) were assayed in normal human and xeroderma pigmentosum (XP) fibroblasts with a monoclonal antibody against these dimers and quantitative fluorescence microscopy. In repair-proficient cells dimer-specific immunofluorescence gradually decreased with time, reaching about 25% of the initial fluorescence after 27 h. Rapid disappearance of dimers was observed in cells which had been microinjected with yeast photoreactivating enzyme prior to UV irradiation. This photoreactivation (PHR) was light dependent and (virtually) complete within 15 min of PHR illumination. In general, PHR of dimers strongly reduces UV-induced unscheduled DNA synthesis (UDS). However, when PHR was applied immediately after UV irradiation, UDS remained unchanged initially; the decrease set in only after 30 min. When PHR was performed 2 h after UV exposure, UDS dropped without delay. An explanation for this difference is preferential removal of some type(s) of nondimer lesions, e.g., (6-4) photoproducts, which is responsible for the PHR-resistant UDS immediately following UV irradiation. After the rapid removal of these photoproducts, the bulk of UDS is due to dimer repair. From the rapid effect of dimer removal by PHR on UDS it can be deduced that the excision of dimers up to the repair synthesis step takes considerably less than 30 min. Also in XP fibroblasts of various complementation groups the effect of PHR was investigated. The immunochemical dimer assay showed rapid PHR-dependent removal comparable to that in normal cells. However, the decrease of (residual) UDS due to PHR was absent (in XP-D) or much delayed (in XP-A and -E) compared to normal cells. This supports the idea that in these XP cells preferential repair of nondimer lesions does occur, but at a much lower rate.
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PMID:Effects of microinjected photoreactivating enzyme on thymine dimer removal and DNA repair synthesis in normal human and xeroderma pigmentosum fibroblasts. 230 42

To extend our knowledge of the excision repair system in mammalian cells we have focussed on the isolation of genes and proteins involved in this process. For the purification and characterization of human repair proteins the microneedle injection assay technique is utilized. This system is based on the transient correction of the excision repair defect of xeroderma pigmentosum (XP) fibroblasts (scored as increase of ultraviolet (u.v.)-induced unscheduled DNA synthesis (UDS) upon microinjection of crude extracts from complementing XP or normal cells. Specific correction is observed in fibroblasts of all (9) excision-deficient XP complementation groups. The XP-A and G correcting factors were found to be proteins and several purification steps (including (NH4)2SO4 fractionation, chromatography of phosphocellulose, heparin and u.v.-irradiated DNA-cellulose) have been worked out for the XP-A correcting protein. The microinjection system was also used for the introduction of (partially) purified repair enzymes of lower organisms. Micrococcus luteus endonuclease and bacteriophage T4 endonuclease V were able to correct all XP complementation groups tested, in marked contrast to the more sophisticated Escherichia coli uvrABC complex injected with uvrD. Photoreversal of dimers could be registered after introduction of the yeast photoreactivating enzyme in repair-competent, XP-variant, XP-C and XP-I fibroblasts (monitored as decrease of (residual) UDS). Remarkably, no effect was noticed in XP-A, D, E and H, suggesting that something prevents dimers in these cells from being monomerized by the injected enzyme. Using DNA-mediated gene transfer we have cloned a human gene (designated ERCC-1) that compensates for the excision defect of the u.v. and mitomycin C-sensitive Chinese hamster ovary cell (CHO) mutant 43-3B (complementation group 2). Characterization of this gene and its cDNA revealed the following features: (1) ERCC-1 corrects the full spectrum of repair deficiencies in mutants of complementation group 2. No correction is observed in mutants of the other CHO complementation groups. (2) The ERCC-1 gene has a size of 15 X 10(3) base-pairs (bp) and consists of 10 exons, one of which appears to be differentially spliced. (3) It encodes two largely identical mRNAs, which differ in the presence or absence of a 72 bp coding exon, situated in the 3' half of the mRNA. Only the cDNA of the large transcript is able to confer repair proficiency to 43-3B cells. No effect of u.v. treatment is found at the level of ERCC-1 transcription in HeLa cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Characterization of genes and proteins involved in excision repair of human cells. 282 Oct 19

Photoreactivation is one of the DNA repair mechanisms to remove UV lesions from cellular DNA with a function of the DNA photolyase and visible light. Two types of photolyase specific for cyclobutane pyrimidine dimers (CPD) and for pyrimidine (6-4) pyrimidones (6-4PD) are found in nature, but neither is present in cells from placental mammals. To investigate the effect of the CPD-specific photolyase on killing and mutations induced by UV, we expressed a marsupial DNA photolyase in DNA repair-deficient group A xeroderma pigmentosum (XP-A) cells. Expression of the photolyase and visible light irradiation removed CPD from cellular DNA and elevated survival of the UV-irradiated XP-A cells, and also reduced mutation frequencies of UV-irradiated shuttle vector plasmids replicating in XP-A cells. The survival of UV-irradiated cells and mutation frequencies of UV-irradiated plasmids were not completely restored to the unirradiated levels by the removal of CPD. These results suggest that both CPD and other UV damage, probably 6-4PD, can lead to cell killing and mutations.
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PMID:Expression of a mammalian DNA photolyase confers light-dependent repair activity and reduces mutations of UV-irradiated shuttle vectors in xeroderma pigmentosum cells. 1060 16