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)

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.
Carcinogenesis 1989 Sep
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

alpha-Acetoxy-N-nitrosopyrrolidine (AcO-NPYR), in the presence of esterase, was reacted with the plasmid pBR322. The AcO-NPYR-treated plasmid was nicked by reaction with spermidine, suggesting the presence of apurinic sites. The treated plasmid also blocked the action of the restriction endonuclease BglI and, to a lesser extent, DraI. The recognition sequences of these restriction enzymes suggest that AcO-NPYR interacts preferentially with guanine and/or cytosine bases in DNA.
Carcinogenesis 1988 Sep
PMID:Interaction of alpha-acetoxy-N-nitrosopyrrolidine with DNA assessed by loss of restriction endonuclease recognition sites and formation of apurinic/apyrimidinic sites. 284 82

This review describes the evolution of research into the genetic basis of how different organisms use the process of excision repair to recognize and remove lesions from their cellular DNA. One particular aspect of excision repair, DNA incision, and how it is controlled at the genetic level in bacteriophage, bacteria, S. cerevisae, D. melanogaster, rodent cells and humans is examined. In phage T4, DNA is incised by a DNA glycosylase-AP endonuclease that is coded for by the denV gene. In E. coli, the products of three genes, uvrA, uvrB and uvrC, are required to form the UVRABC excinuclease that cleaves DNA and releases a fragment 12-13 nucleotides long containing the site of damage. In S. cerevisiae, genes complementing five mutants of the RAD3 epistasis group, rad1, rad2, rad3, rad4 and rad10 have been cloned and analyzed. Rodent cells sensitive to a variety of mutagenic agents and deficient in excision repair are being used in molecular studies to identify and clone human repair genes (e.g. ERCC1) capable of complementing mammalian repair defects. Most studies of the human system, however, have been done with cells isolated from patients suffering from the repair defective, cancer-prone disorder, xeroderma pigmentosum, and these cells are now beginning to be characterized at the molecular level. Studies such as these that provide a greater understanding of the genetic basis of DNA repair should also offer new insights into other cellular processes, including genetic recombination, differentiation, mutagenesis, carcinogenesis and aging.
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PMID:The molecular genetics of the incision step in the DNA excision repair process. 290 Aug 58

Recent studies by others have shown that the endonuclease complex coded for by the uvrA, uvrB and uvrC genes of Escherichia coli (UVR ABC excision nuclease) can incise DNA containing a variety of 'bulk-type' lesions, such as those resulting from u.v. light, (+/-)-7 alpha,8 beta-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE), and N-acetoxy-2-acetylaminofluorene. Using partially purified UVR ABC excision nuclease, we have quantitated the number of endonuclease sensitive sites (ESS) in purified DNA isolated from human fibroblasts treated with u.v. light or BPDE. The number of ESS/10(8) daltons of DNA were calculated from the number average mol. wt. of the DNA as determined by sedimentation in alkaline sucrose gradients. The number of endonuclease sites increased linearly with increasing doses of either u.v. light or BPDE. The UVR ABC excision nuclease was able to incise a majority of the BPDE-DNA adducts. Xeroderma pigmentosum fibroblasts, complementation group A (XP12BE) had 20-25% more ESS at each dose than the BPDE-treated normal (HSBP) cells. Cells treated with 4 microM BPDE and allowed 12 h of incubation to perform excision repair showed removal of 60% of the initial number of ESS from HSBP DNA and 40% of the ESS from XP-A DNA. Beyond 12 h XP12BE cells lost no additional ESS while HSBP cells continued to lose ESS, although at a slower rate, until at 48 h only 22% of the initial ESS remained. In cells treated with 10 J/m2 of u.v. light, the UVR ABC excision nuclease detected 60% of the sites recognized by the pyridimine dimer specific Micrococcus luteus glycosylase/apyrimidinic endonuclease. These results demonstrate the potential use of the UVR ABC excision nuclease in a quantitative assay for determining the number of carcinogen-induced lesions in human DNA.
Carcinogenesis 1986 Jan
PMID:Quantitation of carcinogen-induced DNA damage and repair in human cells with the UVR ABC excision nuclease from Escherichia coli. 308 Feb 55

The photochemical genotoxic and cell-transforming potential of 4-hydroxymethyl-3,3,4-trimethyl-1,2-dioxetane (HTMD) and 3-(N-[4-pyridino]carbamoyl)methyl-3,4,4-trimethyl-1,2-dioxetane , (APD), in mammalian cell was studied. Both dioxetanes, which are efficient sources of triplet-excited ketones on thermal decomposition, induced morphological transformation in Syrian hamster embryo (SHE) fibroblasts. Unscheduled DNA synthesis in SHE and in HeLa cells could not be detected with these dioxetanes, but the number of micronuclei scored after the first mitosis was dose-dependently increased. Single-strand breaks but not Micrococcus luteus u.v.-endonuclease sensitive sites were observed by alkaline elution in HL-60 cells when treated with sub-lethal doses of HTMD and APD. A possible mechanism for the transformation mediated by DNA and chromosomal damage as well as the intermediacy of triplet carbonyls in these events are discussed.
Carcinogenesis 1987 Jul
PMID:Induction of morphological transformation and micronuclei in Syrian hamster embryo fibroblasts by 1,2-dioxetanes. Correlation with single-strand breaks in HL-60 cells. 310 57

The repair of u.v.-induced damage in human and rodent cells was investigated at the level of DNA loops attached to the nuclear matrix. After 2 h post-u.v. incubation, DNase I digestion studies revealed a 3- to 4-fold enrichment of repair-labeled DNA at the nuclear matrix in four xeroderma pigmentosum cell strains belonging to complementation group C. This non-random distribution was not affected by treatment with sodium butyrate. In other cells with limited excision repair, i.e. two xeroderma pigmentosum cell strains of complementation group D and Syrian hamster embryonic cells, as well as in HeLa cells and normal human fibroblasts, no enrichment of repair-labeled DNA at the nuclear matrix was observed. Visualization of repair events in DNA loops by autoradiography of DNA halo-matrix structures confirmed the biochemical observations. The presence or absence of preferential repair of nuclear matrix-associated DNA paralleled the presence or absence of inhomogeneity in the distribution of T4 endonuclease-V-sensitive sites. A detailed analysis of repair events in xeroderma pigmentosum cells of complementation group C showed that after 2 h post-u.v. incubation, repair events were found at both attachment sites in a limited number of loops and that large domains of loops were not subjected to repair.
Carcinogenesis 1986 Jun
PMID:Distribution of u.v.-induced repair events in higher-order chromatin loops in human and hamster fibroblasts. 370 60

Current evidence suggests that the complex nature of mammalian chromatin can result in the concealment of DNA damage from repair enzymes and their co-factors. Recently it has been proposed that the acetylation of histone proteins in chromatin may provide a surveillance system whereby damaged regions of DNA become exposed due to changes in chromatin accessibility. This hypothesis has been tested by: (i) using n-butyrate to induce hyperacetylation in human adenocarcinoma (HT29) cells; (ii) monitoring the enzymatic accessibility of chromatin in permeabilised cells; (iii) measuring u.v. repair-associated nicking of DNA in intact cells and (iv) determining the effects of n-butyrate on cellular sensitivity to DNA damaging agents. The results indicate that the accessibility of chromatin to Micrococcus luteus u.v. endonuclease is enhanced by greater than 2-fold in n-butyrate-treated cells and that there is a corresponding increase in u.v. repair incision rates in intact cells exposed to the drug. Non-toxic levels of n-butyrate induce a block to G1 phase transit and there is a significant growth delay on removal of the drug. Resistance of HT29 cells to u.v.-radiation and adriamycin is enhanced in n-butyrate-treated cells whereas X-ray sensitivity is increased. Although changes in the responses of cells to DNA damaging agents must be considered in relation to the effects of n-butyrate on growth rate and cell-cycle distribution, the results are not inconsistent with the proposal that increased enzymatic-accessibility/repair is biologically favourable for the resistance of cells to u.v.-radiation damage. Overall the results support the suggested operation of a histone acetylation-based chromatin surveillance system in human cells.
Carcinogenesis 1986 Mar
PMID:n-Butyrate alters chromatin accessibility to DNA repair enzymes. 375 5

Escherichia coli endonuclease IV was used to incise cellular DNA specifically at apurinic/apyrimidinic (AP) sites prior to alkaline elution to measure the resulting DNA strand breaks. gamma-Irradiated HeLa cells initially contained DNA strand breaks and no AP sites. Upon incubation at 37 degrees C the strand breaks were rapidly repaired and AP sites were generated and subsequently repaired. The transient nature of the AP sites indicates the in vivo operation of a base excision repair pathway whereby damaged bases are removed from DNA by DNA glycosylases to produce AP intermediates that are then substrates for AP endonucleases.
Carcinogenesis 1987 Apr
PMID:Base excision repair of DNA in gamma-irradiated human cells. 382 22

Homozygous xeroderma pigmentosum fibroblasts cannot repair damage to DNA bases, but can repair damage that involves chain breaks. In xeroderma pigmentosum, therefore, there is a defect in an early step in repair at which base damage is recognized and the polynucleotide chain broken enzymatically (by an endonuclease). Heterozygous fibroblasts repair base damage to normal extents. Carcinogenesis in xeroderma pigmentosum, and perhaps in some normal individuals, may be the result of somatic mutations caused by unrepaired damage.
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PMID:Xeroderma pigmentosum: a human disease in which an initial stage of DNA repair is defective. 525 33

The DNA repair endonuclease activity has been studied in several xeroderma pigmentosum (XP) cell lines of complementation groups A and C. phi X174 RFI DNA treated with u.v.-light or OsO4 was used as a substrate. All XP cells tested appeared to lack this enzyme compared to control cells. However, when extracts from complementation groups A and C were mixed, activity levels close to that of the control cells were found, clearly indicating that the two cell lines can complement each other with regard to the DNA repair endonuclease activity. The XP cells were found to contain normal levels of AP-endonuclease.
Carcinogenesis 1984 Jun
PMID:Xeroderma pigmentosum: in vitro complementation of DNA repair endonuclease. 623 45


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