Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have used a T4 endonuclease V assay method for UV-induced pryrimidine dimers in cellular DNA in vivo to obtain evidence for recombinational DNA exhanges after UV irradiation of normal human and Xeroderma pigmentosum (XP) cells. Our data indicate that the endonuclease-sensitive sites in excision-defective XP cells are removed very slowly from the irradiated parental strands and appear concomitantly in daughter strands newly synthesized during post-UV incubation. In the defective XP cells, the extent of appearance of sensitive sites in daughter strands synthesized during a period of 24 h after 10 J/m2 appears to be small, probably less than 15% of the initial number of sensitive sites detected in cellular parental strands. Demonstration of such exchanges between normal-density parental and 5-bromodeoxyuridine-labeled daughter strands by alkaline CsCl isopycnic centrifugation was unsuccessful. Further, the extent is much lower in normal human cells because of their efficient excision repair of the dimers before and after exchanges than in the defective XP cells.
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PMID:Low-level DNA exchanges in normal human and xeroderma pigmentosum cells after UV irradiation. 86 96

A DNA-binding protein specific for ultraviolet irradiated DNA has been purified extensively from human placenta. The binding preparation is free of exonuclease, polymerase, endonuclease, and N-glycosidase activity. The binding activity is salt dependent and is specific for double-stranded irradiated DNA. DNA from which the pyrimidine dimers have been monomerized by the action of photolyase (photoreactivating enzyme) remains an effective substrate for the binding protein, suggesting that the protein recognizes photoproducts other than pyrimidine dimers. This is supported by the finding that DNA irradiated under conditions which introduce only pyrimidine dimers is not a substrate for the binding protein. Examination of three of the xeroderma pigmentosum complementation groups has revealed no deficiency in this binding activity.
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PMID:A DNA binding protein from human placenta specific for ultraviolet damaged DNA. 127 48

The molecular basis of xeroderma pigmentosum (XP) group A was studied and 3 nonsense mutations of the XP-A complementing gene (XPAC) were identified. One was a nucleotide transition altering the Arg-228 codon (CGA) to a nonsense codon (TGA). This transition creates a new cleavage site for the restriction endonuclease HphI. Of 21 unrelated Japanese XP-A patients examined, 1 (XP39OS) was a homozygote for this mutation and 3 were compound heterozygotes for this mutation and for the splicing mutation of intron 3 reported previously which is the most common mutation in Japanese patients and creates a new cleavage site for the restriction endonuclease AlwNI. The second mutation was a nucleotide transition altering the Arg-207 codon (CGA) to a nonsense codon (TGA). A Palestinian patient (XP12RO) who had severe symptoms of XP was homozygous for this mutation. The third mutation was a nucleotide transversion altering the Tyr-116 codon (TAT) to a nonsense codon (TAA). This transversion creates a new cleavage site for the restriction endonuclease MseI. Of the Japanese patients, 2 with severe clinical symptoms had this mutant allele. One was a compound heterozygote for this mutation and for the splicing mutation, and the other was heterozygous for this mutation and homozygous for the splicing mutation. Although most XP-A patients such as XP12RO have severe skin symptoms and neurological abnormalities of the de Sanctis-Cacchione syndrome, patient XP39OS was an atypical XP-A patient who had mild skin symptoms and minimal neurological abnormalities. Our results suggest that the clinical heterogeneity in XP-A is due to different mutations in the XPAC gene. Moreover, our data indicate that almost all Japanese cases of XP-A are caused by one or more of the 3 mutations, i.e., the splicing mutation of intron 3 and the 2 nonsense mutations of codons 116 and 228. Therefore, by restriction fragment length polymorphism analysis of PCR-amplified DNA sequences using the 3 restriction enzymes described above, rapid and reliable diagnosis of XP-A can be achieved in almost all Japanese subjects including prenatal cases and carriers.
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PMID:Three nonsense mutations responsible for group A xeroderma pigmentosum. 137 2

The denV gene from bacteriophage T4 encodes a pyrimidine dimer-specific endonuclease that has the capacity to initiate excision repair of DNA. Cells from excision repair-deficient xeroderma pigmentosum (XP) patients are able to carry out excision repair initiated by the denV gene product and introduction of the denV gene into XP cells results in the partial restoration of colony-forming ability after irradiation with UV light. In this work we have constructed a helper-independent recombinant human adenovirus, Ad5denV, which contains the denV gene. A 1.9 kb cartridge consisting of the denV gene flanked by the long terminal repeat (LTR) promoter from Rous sarcoma virus (RSV) and the simian virus 40 (SV40) polyadenylation (poly A) splice signals, was inserted into the E3 region of an E3 deletion mutant (Ad5d1E3) of adenovirus type 5. Infection of human fibroblasts and other permissive human cells with Ad5denV resulted in lytic infection and expression of the denV gene was confirmed by primer extension of infected cell RNA. The ability of the denV gene to restore the DNA repair deficiency in XP fibroblasts was examined using host cell reactivation of viral structural antigen formation for UV-irradiated adenovirus. The control virus, Ad5VSV, was also a recombinant which contained the gene for vesicular stomatitis virus glycoprotein G inserted into the E3 region of Ad5d1E3. UV survival of Ad5denV was similar to that of Ad5VSV following infection of two normal fibroblast strains and a Cockayne syndrome fibroblast strain, CS7SE, from complementation group B. In contrast, UV survival of Ad5denV was significantly greater than that for Ad5VSV after infection of three unrelated XP fibroblast strains from complementation groups A, C and E. However, UV survival of Ad5denV in the XP fibroblasts did not reach levels obtained in normal fibroblasts, indicating that restoration of the XP defect was partial.
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PMID:Construction of a recombinant adenovirus containing the denV gene from bacteriophage T4 which can partially restore the DNA repair deficiency in xeroderma pigmentosum fibroblasts. 170 21

The extent of DNA excision repair was determined in dermal fibroblast strains from clinically normal and xeroderma pigmentosum (XP; complementation group A) human donors after single or combined exposures to 254-nm ultraviolet light and 4-nitroquinoline 1-oxide (4NQO). The repair was monitored by incubation of the treated cultures in the presence of 1-beta-D-arabinofuranosylcytosine (araC), a potent inhibitor of long-patch excision repair, followed by quantitation of araC-accumulated DNA single-strand breaks (representing repair events) by velocity sedimentation analysis in alkaline sucrose gradients. The amount of repair in normal fibroblast strains increased as a function of UV fluence and reached a plateau at 15 J/m2; strand breaks were not detected when these same cultures were irradiated with as much as 60 J/m2 UV and incubated in the absence of araC, implying that an initial (incision) step is rate-limiting in the repair of UV damage. In normal fibroblasts (i) the incidence of araC-detectable lesions removed during fixed intervals following exposure to 4NQO (4 microM; 30 min) was approximately 2.5 times greater than that seen following irradiation with repair-saturating fluences (greater than or equal to 15 J/m2) of UV-rays; and (ii) the amount of repair in cultures treated simultaneously with 4NQO (0.5-6 microM; 30 min) and a repair-saturating fluence of UV (20 J/m2) was found to approach the sum of that arising from exposure to each separately. The XP cells (XP12BE) exhibited a deficiency in the removal of araC-detectable DNA lesions following exposure to either of the carcinogens. Since araC is known to inhibit the repair of alkali-stable 4NQO-DNA adducts (i.e., lesions assumed to be removed by the UV-like excision pathway) but not that of alkali-labile sites (i.e., DNA lesions operated on by the X-ray-like repair pathway), our results strongly imply that the multistep excision-repair pathway operative on UV photoproducts in human fibroblasts differs from that responsible for removing alkali-stable (araC-detectable) 4NQO adducts by at least one step, presumably the rate-limiting incision reaction mediated by a lesion-recognizing endonuclease.
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PMID:Differential repair of 1-beta-D-arabinofuranosylcytosine-detectable sites in DNA of human fibroblasts exposed to ultraviolet light and 4-nitroquinoline 1-oxide. 190 30

The contribution of DNA damage to the effects of 193-nm excimer laser radiation on mammalian cells in culture was studied in order to evaluate the mutagenic potential of this UV wavelength in vivo. Two approaches were taken: measurement of pyrimidine dimer-specific endonuclease-sensitive sites/megabase and comparison of the 193-nm radiation-induced cytotoxicity in normal versus DNA repair-deficient cells. The formation of pyrimidine dimer-specific endonuclease-sensitive sites/megabase was inversely related to the thickness of the cytoplasm overlying the nuclei of normal human fibroblasts (NHF) and Chinese hamster ovary cells. The results of these measurements and a calculation of the absorption coefficient of cytoplasm indicate that each 1 micron of cytoplasm attenuates the incident radiation by greater than 90% and, therefore, the nuclear DNA in tissue will be highly protected from 193-nm radiation by overlying cytoplasm. The reduction in colony-forming ability induced by 254-nm, 193-nm, and X-ray radiation was measured in NHF, xeroderma pigmentosum (group A) cells, and ataxia telangiectasia cells. Xeroderma pigmentosum (group A) cells were 16.5 times more sensitive to 254-nm radiation but only 3.5 times more sensitive to 193-nm radiation than NHF cells, indicating that cyclobutylpyrimidine dimers were not the major lethal lesion formed at 193 nm. AT cells were 3.4 times more sensitive to X-rays than NHF cells, but these cell types were almost equally sensitive to 193-nm radiation, indicating that 193 nm did not induce the same type of lethal lesions as X-rays.
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PMID:DNA damage induced by 193-nm radiation in mammalian cells. 198 91

Cells from patients with the cancer-prone inherited disease, xeroderma pigmentosum (XP) are known to be defective in the endonuclease-mediated incision step in excision repair of a number of different types of DNA adducts, but the molecular events responsible have not been delineated. We have previously reported isolation of two DNA endonucleases, pI 4.6 and 7.6, from normal human chromatin which recognize adducts produced by psoralen plus long wavelength ultraviolet radiation (UVA). These endonucleases are both present in XP complementation group A (XPA) cells even though these cells are hypersensitive to this type of damage. We now report that introduction by electroporation of either normal endonuclease into XPA cells restored their markedly deficient DNA repair-related unscheduled DNA synthesis (UDS) to higher than normal levels following exposure to psoralen plus UVA. Introduction of XPA endonucleases into similarly treated XPA cells had little or no restorative effect on UDS. However, both normal and XPA endonucleases increased UDS in normal cells to higher than normal levels. These results indicate that XPA cells have endonucleases which can repair these adducts but which cannot function in intact cells unless a factor(s), which they lack is provided by normal cells.
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PMID:Electroporation of normal human DNA endonucleases into xeroderma pigmentosum cells corrects their DNA repair defect. 231 Nov 96

The limited DNA-excision repair in UV-irradiated nondividing fibroblasts from xeroderma pigmentosum complementation group C (XP-C) occurs in localized chromatin regions generating large DNA segments (at least 30-70 kb) free of pyrimidine dimers. A genomic fraction enriched for this DNA was isolated on the basis of the larger size of the repaired fragments after UV-endonuclease treatment and screened for specific genes. It contains more copies per microgram DNA of two transcriptionally active genes, beta-actin and dihydrofolate reductase, compared to the remaining DNA but an equal number of copies per microgram DNA of an inactive locus termed 754. We confirmed that the active genes were preferentially repaired by measuring the removal of pyrimidine dimers from specific genomic restriction fragments comprising these sequences. These results mean that a unique set of relatively large chromatin domains are repaired in nondividing XP-C cells, even though most of the DNA remains unrepaired. The repaired domains may be those containing the active genes. This specific repair may account for the relatively high UV-resistance of the nondividing cells. In normal cells, a very rapid repair of a restriction fragment containing the beta-actin gene and slow repair of the 754-containing fragment was detected indicating that a similar domain-oriented repair process also exists in these cells. These results are consistent with the previously discovered rapid repair of active genes compared to bulk DNA. Separate damage-recognition systems may exist in human cells for chromatin domains that contain transcribed regions and those that contain no transcribed regions. The latter system may be deficient in XP-C.
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PMID:Selective repair of specific chromatin domains in UV-irradiated cells from xeroderma pigmentosum complementation group C. 234 4

Human fibroblasts were embedded in microscopic-sized agarose beads and lysed in situ to produce chromosome-sized DNA trapped inside the beads. Conventional alkaline agarose gel electrophoresis of trapped DNA from cells damaged by X-rays before embedding gave mol. wts similar to those obtained with alkaline sucrose gradients. When cells were irradiated with UV light before embedding in agarose and incubated with UV endonuclease to cleave cyclobutane pyrimidine dimer sites, UV damage was detectable by gel electrophoresis over a range of 2.6-52 J/m2 as a linear function of dose, and repair was detectable within 6 h of irradiation. Two independently derived UV-resistant xeroderma pigmentosum (XP) revertants did not remove cyclobutane dimers up to 48 h after irradiation. Incubation of normal and XP revertant cells with cytosine arabinoside after UV irradiation resulted in similar numbers of single-strand breaks; these breaks represent repair of non-dimer photoproducts. Evidently, excision of cyclobutane pyrimidine dimers from the whole genome is not necessary for survival of human cells after UV irradiation; rather, repair of non-dimer photoproducts such as photoproducts in the genome as a whole or cyclobutane dimers in a small number of genes may be more biologically important.
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PMID:DNA damage and repair in normal, xeroderma pigmentosum and XP revertant cells analyzed by gel electrophoresis: excision of cyclobutane dimers from the whole genome is not necessary for cell survival. 276 60

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


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