Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.5.1.2 (DNA ligase)
 2,749 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Since interferon inducible 2',5'-oligoadenylate (2,5An) synthetase activity is present in a wide variety of cells and is affected by various hormonal conditions, primary human mammary tumor extracts were examined for the constitutive presence of this enzyme and its possible relationship with the various hormonal receptor levels in these tissues. Further, since 2,5An synthetase has been implicated as a possible factor controlling cell replication, we assayed DNA polymerases in these same tumor extracts to determine any correlation between 2,5An synthetase activity and growth potential. A survey of the soluble extracts from 24 different surgically removed human mammary tumor specimens for 2,5An synthetase activity indicated that this enzyme was indeed present in all extracts but in widely varying amounts of activity (31-2,666 nmol adenosine 5'-phosphate incorporated/mg protein). The 2,5An synthesized in the enzymic reactions ranged in size from di- to hexamers, with trimers being the abundant 2,5An in the majority of tumors. A comparison of the assay results for estrogen and progestin receptors with 2,5An synthesis indicated that high 2,5An synthetase activity was found in both estrogen or progestin positive and negative tumors. Thus, 2,5An synthetase activity was unrelated (r = 0.329 and 0.077, respectively, for estrogen and progestin receptors) to the hormonal receptor content of these tumors. A similar comparison was made between 2,5An synthesis and assay results for the activities of DNA polymerase alpha, regarded as the principal DNA replicating enzyme, and DNA polymerase beta, regarded as the DNA repair enzyme. Although the activity of the polymerases were also quite varied, the majority of tumor extracts demonstrated higher alpha polymerase activity with no parallel difference between the alpha and beta enzymes. There was, however, a weak correlation (r = 0.751) between 2,5An synthetase activity and DNA polymerase alpha activity among the tumors examined. Less of a correlation existed with DNA polymerase beta activity (r = 0.600). These results suggested that the potential of the tumors to synthesize 2,5An was unrelated to their hormonal responsiveness and only weakly related to their growth potential reflected by DNA polymerase alpha activity.
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PMID:2',5'-oligoadenylate synthetase activity in human mammary tumors and its potential correlation with tumor growth or hormonal responsiveness. 377 41

The biosynthesis of the human DNA repair enzyme uracil-DNA glycosylase has been characterized by the reaction of in vitro- and in vivo-produced protein with an anti-human placental uracil-DNA glycosylase monoclonal antibody. In vitro synthesis of the DNA repair enzyme was examined after the translation of human placental polyadenylated [poly(A)+] RNA by immunoprecipitation of the [35S]methionine-labeled translation products. As defined by sucrose density analysis, immunoprecipitable in vitro products were translated from 16S poly(A)+ RNA and 11S poly(A)+ RNA. While the products of the 11S poly(A)+ RNA were smaller than purified uracil-DNA glycosylase, the product of the 16 S poly(A)+ RNA had a molecular weight of 37,000, identical to the size previously observed for purified human placental uracil-DNA glycosylase. Immunoblot analysis of human placental cell extracts and of normal human fibroblast cell extracts demonstrated the recognition of one Mr 37,000 protein. Immunoprecipitation of [35S]methionine-labeled normal human cell extracts with the anti-glycosylase monoclonal antibody specifically detected only the Mr 37,000 uracil-DNA glycosylase protein. Pulse-chase analysis demonstrated that the 35S radioactivity in the Mr 37,000 uracil-DNA glycosylase decreased over a 5-h interval. These results show that immunoreactive human uracil-DNA glycosylase protein was synthesized at its enzymatically active molecular weight of 37,000 as the primary translation product of a 16S polyadenylated messenger RNA.
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PMID:Biosynthesis of the human base excision repair enzyme uracil-DNA glycosylase. 379 Nov 99

Mex+ human lymphoma cell lines contain O6-methylguanine-DNA methyltransferase, a DNA repair enzyme that undergoes suicide inactivation on interaction with its substrate. The cells are therefore competent to remove the alkylation lesion O6-methylguanine from their DNA. However, several repair-deficient lymphoma cell lines (Mex-) are also known. It is shown here that Mex+ cells can be converted temporarily to a Mex- phenotype by growth in nontoxic concentrations of free O6-methylguanine. The depletion of methyltransferase activity is not a result of O6-methylguanine incorporation into DNA and subsequent demethylation by the enzyme. It is proposed that O6-methylguanine is mistakenly incorporated into tRNA molecules by means of a post-transcriptional ribosyl transfer reaction. The demethylation of such bases in tRNA has been demonstrated by using bacterial and human DNA repair enzymes. The existence of such a subversive repair of a methylated base in tRNA raises the possibility of competition between DNA and RNA for cellular DNA repair enzymes. Furthermore, it is proposed that the known aberrant methylation of tRNA in certain transformed cells, together with subversive tRNA repair, could account for the Mex- phenotype.
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PMID:Possible depletion of a DNA repair enzyme in human lymphoma cells by subversive repair. 386 Aug 61

The denV gene of phage T4, encoding the pyrimidine dimer-specific DNA repair enzyme endonuclease V, has been introduced by DNA transfection into the UV-sensitive DNA repair-deficient Chinese hamster ovary (CHO) cell line UV5. Transformants were first selected for resistance to the antibiotic G418 conferred by the neo gene from Tn5 carried by the same plasmid. A majority of the isolated G418-resistant UV5 clones also showed an increased resistance to 254-nm UV light. One clone, designated I-A1, was found to have an intermediate level of colony-forming ability after UV irradiation when compared to UV5 and wild-type AA8 cells. A Southern blot showed that I-A1 carries a single integrated intact copy of the denV gene. Alkaline sucrose gradients revealed a dose-dependent appearance of breaks in the DNA of I-A1 cells following UV-irradiation, while unirradiated cells did not exhibit any significant breaks. Analysis of DNA repair by isopycnic sedimentation showed that DNA excision repair by I-A1 was at least equal to the level of repair in AA8 cells. These results show that the prokaryotic denV gene can restore UV repair capabilities in vivo to CHO UV5 cells defective in repair of UV-induced damage.
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PMID:Genetic complementation of UV-induced DNA repair in Chinese hamster ovary cells by the denV gene of phage T4. 386 86

The inducible resistance to alkylation mutagenesis and killing in Escherichia coli (the adaptive response) is controlled by the ada gene. The Ada protein acts both as a positive regulator of the response and as a DNA repair enzyme, correcting premutagenic O6-alkylguanine in DNA by suicidal transfer of the alkyl group to one of its own cysteine residues. We have determined the DNA sequence of the cloned ada+ gene and its regulatory region. The data reveal potential sites of ada autoregulation. Amino acid sequence determinations show that the active center for the O6-methylguanine-DNA methyltransferase is located close to the polypeptide COOH terminus and has the unusual sequence -Pro-Cys-His-, preceded by a very hydrophobic region. These same structural features are present at the active site of thymidylate synthase, suggesting a common chemical mechanism for activation of the cysteine.
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PMID:Active site and complete sequence of the suicidal methyltransferase that counters alkylation mutagenesis. 388 9

O6-Methylguanine-DNA methyltransferase, a DNA repair enzyme which transfers the methyl group of O6-methylguanine residue to a cysteinyl residue in the methyltransferase itself, was examined in rat organs by quantifying the S-methylcysteine formed in the methyl acceptor protein. Among the various organs examined, the spleen exhibited the highest enzyme specific activity followed by the thymus, liver, lung and testis. Brain had the lowest activity. The patterns of subcellular distribution of the methyltransferase in spleen and liver were different: while 75-80% of the activity was present in the nuclear fraction of the spleen, 54% of the activity in the liver was found in the nuclei and 35% in the cytosolic fraction. Forty-five and thirty-five percent of the total nuclear enzyme activity could be extracted with 1 M and 2 M NaCl solutions, respectively, indicating that the repair enzyme is not tightly bound to the nuclear matrix. When isolated nuclei were incubated with [methyl-3H]DNA substrate and subsequently fractionated into histone and non-histone protein fractions, over 90% of the radioactivity was coeluted on a Bio-Rex 70 column with the non-histone fraction and only a negligible amount of radioactivity was found to be associated with the histone fraction. The molecular mass of the [methyl-3H]methyltransferase in the non-histone fraction was determined to be 23,000, and its pI value was found to be 6.6 by two-dimensional polyacrylamide gel electrophoresis.
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PMID:Studies on the distribution of O6-methylguanine-DNA methyltransferase in rat. 394 77

DNA polymerase beta levels were measured in 4 cell lines of normal human skin fibroblasts and in 5 cell lines of skin fibroblasts from patients with ataxia telangiectasia, an autosomal recessive disease exhibiting marked X-ray sensitivity. The enzyme specific activities for the normal lines were similar and the mean value was 2-fold lower than the mean value for the ataxia lines. With both kinds of cells, the enzyme level did not change as the cultures progressed from logarithmic to stationary phase of growth. Thus, this putative DNA repair enzyme appears to be 'constitutive' in human skin fibroblast lines, and a modest elevation of beta-polymerase activity is associated with ataxia telangiectasia. These results are discussed in the context to current views about DNA-repair enzymes in X-ray-sensitive cultured mammalian cells.
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PMID:Measurement of DNA polymerase beta in skin fibroblast cell lines from patients with ataxia telangiectasia. 405 46

Lipid peroxidation aldehydes of the 4-hydroxy-alpha, beta-unsaturated type, as well as the tobacco-smoke related alpha, beta-unsaturated aldehyde, acrolein, were highly cytotoxic and decreased the intracellular thiol content in cultured human bronchial fibroblasts after treatment with micromolar concentrations. In comparison, formaldehyde and acetaldehyde were less toxic and 100- to 300-fold higher doses were required to affect cell survival or thiol levels. The unsaturated aldehydes also markedly inhibited the DNA repair enzyme O6-methylguanine-DNA methyltransferase known to have a cysteine residue in its active site, but had no effect on the activity of uracil-DNA glycosylase. Our results indicate that reactive aldehydes of either exogenous or endogenous origin have direct cytotoxic effects and may also make cells more susceptible to other toxic chemicals due to an impairment in cellular defense mechanisms, e.g., DNA repair and detoxification by systems requiring glutathione.
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PMID:Cytotoxicity, thiol depletion and inhibition of O6-methylguanine-DNA methyltransferase by various aldehydes in cultured human bronchial fibroblasts. 406 50

The enhancement of tumor development following acute stress has been demonstrated in some animal studies. This study was designed to explore mechanisms that would account in part for the relationship between stress and tumor development at the level of DNA repair, using a rat model. Forty-four rats were given the carcinogen dimethylnitrosamine in their drinking water, and half were randomly assigned to a rotational stress condition. The levels of methyltransferase, a DNA repair enzyme induced in response to carcinogen damage, were significantly lower in spleens from the stressed animals. These data suggest that stress may impair DNA repair.
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PMID:Effects of stress on methyltransferase synthesis: an important DNA repair enzyme. 407 16

With the alkaline sucrose gradient centrifugation method, it was found that dormant spores of Clostridium botulinum subjected to 300 krads of gamma radiation showed a distinct decrease in deoxyribonucleic acid (DNA) fragment size, indicating induction of single-strand breaks (SSB). A two- to threefold difference in radiation resistance of spores of two strains of C. botulinum, 33A (37% survival dose [D(37)] = 110 krads) and 51B (D(37) = 47 krads), was accompanied by relatively larger DNA fragments (molecular weight 7.9 x 10(7)) obtained during extraction from the radiation-resistant strain 33A and smaller DNA fragments (molecular weight 1.8 x 10(7)) obtained under identical conditions from radiation-sensitive strain 51B. The apparent number of DNA SSB produced by 300 krads in strains 33A and 51B was 0.37 and 3.50, respectively, per 10(8) daltons of DNA. Addition of 0.02 M ethylenediaminetetraacetic acid (EDTA) to spore suspensions during irradiation doubled the apparent number of SSB in strain 33A but had no effect on strain 51B. In vivo, 0.02 M EDTA present during irradiation to 100 to 300 krads decreased survival of spores of 33A by about 30% but had little or no effect on 51B. Survival of 33A was also reduced by about 45% when the spores were irradiated while frozen in dry ice (-75 C) and, after irradiation, immediately exposed to 0.03 M EDTA for 1 h to inhibit repair in the dormant spores. These results suggest that the highly radiation-resistant strain 33A may be able to accomplish repair of SSB during irradiation or after irradiation under nonphysiological conditions, i.e., in the dormant state. This repair can be inhibited by EDTA. Sedimentation patterns show that DNA from spores of both strains 33A and 51B did not show any postirradiation repair during the first 6 h of germination, as opposed to Bacillus subtilis spores, which exhibit repair immediately after germination. These observations suggest the existence of direct repair in physiological dormant spores of strain 33A in the cryptobiotic resting state in the absence of germination. The repair seems to be similar to that of polynucleotide ligase activity shown to be operative in some vegetative cells. Apparently radiation-sensitive strains such as 51B and B. subtilis are generally poor in DNA repair enzyme activity under conditions of spore dormancy, which may account for the approximately threefold difference in radiation sensitivity or DNA fragility of different strains, or both.
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PMID:Direct enzymatic repair of deoxyribonucleic acid single-strand breaks in dormant spores. 420 67


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