Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.7 (DNA polymerase)
17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ether-permeabilized (nucleotide-permeable) Escherichia coli cells exhibited DNA excision repair when exposed to the following carcinogenic K-region epoxides: 7-methyl- and 7,12-dimethyl-benz[a]anthracene-5,6-oxide, chrysene-5,6-oxide and benzo[a]pyrene-4,5-oxide. This DNA excision repair was missing in uvr A and uvr B mutant cells. The K-region epoxide phenanthrene-9,10-oxide was ineffective in all E. coli strains tested. In contrast to the K-region epoxides which where found active only in wild type cells, 1,2,3,4-diepoxybutane and the 6,7-epoxides of the tumor promoter TPA (12-O-tetradecanoyl-phorbol-13-acetate) elicited DNA repair in uvrA, uvrB mutant cells as well. Enzymic activities catalyzing particular repair steps were identified by determining a) repair polymerization and b) size reduction of denatured DNA. A) An easily quantifiable effect in E. coli wild type cells was epoxide-induced repair polymerization. None of the K-region epoxides tested stimulated DNA repair synthesis in uvrA, uvrB mutant cells, indicating that the uvrA-, uvrB-controlled UV-endonuclease initiated excision repair by cleaving epoxide-damaged DNA. 1,2,3,4-Diepoxybutane and the TPA-6,7-oxides induced DNA repair polymerization in uvr-deficient cells, although to a lesser extent than in wild type cells, suggesting the involvement of uvr-independent incision steps. None of the epoxides induced repair polymerization in a mutant (polA107) lacking the 5'--3'exonucleolytic activity of DNA polymerase I (exonuclease VI). The absence of any repair polymerization in the polA107 mutant indicates that the exonuclease VI plays a central role in removing epoxide-damaged nucleotides. As evidenced by greatly reduced levels of repair polymerization measured in polA1 cells, DNA polymerase I was the main polymerizing enzyme. b) As a consequence of treatment with 7-methyl-benz[a]anthracene-5,6-oxide, DNA from wild type cells, contrary to uvrA mutant cells, showed size reduction after denaturation and sedimentation in alkaline sucrose gradients. This is explained by repair-specific endonucleolytic cleavage of damaged DNA. The incision required the presence of ATP indicating that functional UV-endonuclease needs ATP as a cofactor.
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PMID:Carcinogen-induced DNA repair in nucleotide-permeable Escherichia coli cells. Analysis of DNA repair induced by carcinogenic K-region epoxides and 1,2,3,4-diepoxybutane. 15 97

Ether-permeabilized (nucleotide-permeable) Escherichia coli cells respond to alkylating and arylalkylating carcinogens with DNA excision repair, as assessed by their stimulation of DNA repair synthesis. In the present work, we have investigated whether DNA repair synthesis in ether-treated E. coli cells can serve as a general indicator to monitor the DNA-binding of carcinogens, mutagens and antitumor agents. Therefore, a standard assay was developed and comparative analyses were performed on 11 ultimate carcinogens, 10 proximate carcinogens, 2 tumor promoters, 6 mutagens, and 12 antitumor agents. All ultimate carcinogens (alkylating, acylating, arylalkylating agents) and mutagens (e.g., hydrogeen peroxide, acridine derivatives) caused DNA excision repair in wild type cells as measured by [3H] dTMP incorporation and simultaneously inhibited replicative DNA synthesis to various extents. Control experiments with the mutant cells uvrA and uvrB were performed to determine whether the pyrimidine-dimer-specific UV-endonuclease was involved in the removal of DNA damage. This was found to be true for the ultimate carcinogens (Ac)2 ONFln, mitomycin C, and for very reactive alkylating carcinogens. None of the ultimate carcinogens induced repair polymerization in mutant cells lacking the 5'-3' exonucleolytic activity of DNA polymerase I. Proximate carcinogens, such as Me2NNO, 4-nitroquinoline-1-oxide and aflatoxins, did not induce excision repair in the standard assay, probably because of the inability of E. coli to perform the activation steps necessary for covalent DNA-binding. However, Me2NNO, when pretreated with Udenfriend's hydroxylating mixture, gave rise to a low level of repair polymerization in ether-treated cells. Intercalating mutagens, such as quinacrine and ethidum bromide, inhibited replicative DNA synthesis. However, they were not found to be repair-inducers. THE TUMOR PROMOters TPA and phorbol-12,13-didecanoate did not cause excision repair, even when applied at high concentrations, nor did they inhibit repair synthesis stimulated by MeNOUr or (Ac)2 ONFln. The antitumor agents may be classified into two groups on the basis of the influence they exert on DNA synthesis: members of the first group (involving BCNU and bleomycin) stimulate repair polymerization and, in addition, inhibit DNA replication. These compounds are known to bind covalently to DNA. The second group of drugs (including adriamycin and cis-Pt(II)diammine complexes) inhibits DNA replication without stimulating repair synthesis. The predominant DNA-interaction of these compounds is known to be a non-covalent (i.e., intercalative, electrostatic) binding. Our experiments show that the ether-permeabilized E. coli cell can be successfully used to test ultimate carcinogens, mutagens and antitumor agents for repair-inducing and replication-inhibiting activity. The standard test might be extended to pre- and proximate carcinogens, provided these can be suitably activated.
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PMID:The nucleotide-permeable Escherichia coli cell, a sensitive DNA repair indicator for carcinogens, mutagens, and antitumor agents binding covalently to DNA. 15 98

The effects of the anthracycline antiboties, daunomycin and adriamycin, on the DNA-directed activities of DNA polymerases from murine sarcoma virus, rat liver (high-molecular-weight species), Escherichia coli, and Micrococcus luteus were determined. Under all conditions tested, these compounds had greater inhibitory effect against the viral polymerase than against cellular polymerase. The inhibition of murine sarcoma virus DNA polymerase by daunomycin was competitive with respect to DNA. For viral DNA polymerase it was concluded that the inhibition was predominatly caused by the interaction of duanomycin with the primer-template DNA. Also, an appreciable reversal of the daunomycin-induced inhibition of this polymerase by an increase in Mg-2+ concentration is consistent with the conclusion derived by competition experiments. In contrast, the inhibition of both rat liver and M. luteus DNA polymerases was essentially noncompetitive with DNA. Also, bacterial enzymes wer e less sensitive to inhibition by these drugs than the virion polymerase. The strong and preferential inhibiton of viral DNA polymerase is discussed in relation to a differential sensitivity of normal as compared to tumor cells observed in some cell lines.
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PMID:A comparison of the effects of daunomycin and adriamycin on various DNA polymerases. 16 90

Extracts of Novikoff hepatoma cells contain factors capable of stimulating in vitro DNA synthesis several fold. The activity can be resolved into three separate protein peaks on DEAE-Sephadex. Two of these, factors II and III, have been purified and partially characterized. Both factors increase the initial rate of DNA synthesis and allow synthesis to proceed much longer. If either factor is added after synthesis by the DNA polymerase has reached a plateau, resumption of synthesis occurs. The factors appear to have different modes of action or sites of action since they show an additive effect even when a single one is used at saturating conditions. These factors are present in normal rat liver but at a concentration less than 5% of that found in the tumor cells. When tested with several highly purified DNA polymerases (DNA nucleotidyltransferase, EC 2.7.7.7), the factors show a much greater stimulation of homologous, non-mitochondrial enzymes (rat liver nuclear-, rat liver cytoplasmic-, or Novikoff-DNA polymerases) when compared with rat liver or calf liver mitochondrial-, Escherichia coli I-, or sea urchin nuclear-DNA polymerases. The mechanism of action of these factors is not known at present. No enzymatic activity has been associated with factor III. Highly purified, but not homogeneous, preparations of factor II contain low levels of endonuclease; it has not been established whether endonuclease is a contaminant or is responsible for the stimulating activity.
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PMID:Stimulation of DNA polymerase by factors isolated from Novikoff hepatoma. 16 86

We have described the in vitro isolation of type-C RNA viruses from two outbreaks of a fatal neoplastic disease in turkeys we diagnosed as reticuloendotheliosis. The virus had a density of 1.16 g/ml in sucrose gradients, had a DNA polymerase capable of using both endogenous and exogenous (synthetic) templates, and was infectious in vitro for turkey and chick cells. The culture-propagated virus was oncogenic for turkeys. The virus isolates were unrelated to avian leukosis virus and antigenically identical to reticuloendotheliosis virus (REV) strain T. Thus our studies suggested that REV is a causative agent of naturally occurring, fatal leukosis in turkeys.
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PMID:Isolation and characterization of viruses from natural outbreaks of reticuloendotheliosis in turkeys. 16 89

Incorporation of [3H]TTP into membrane-denuded nuclei and fractions of these nuclei from host liver and Morris hepatomas has been compared. Treatment of sucrose nuclei with Triton X-100 removed 95% of the phospholipids and 15 to 20% of the protein. These membrane-denuded nuclei remained physically stable. The Triton X-100-extracted nuclei incorporated label into their DNA in nuclear-incorporating system similar to sucrose nuclei with their membranes intact. Triton X-100-treated nuclei from hepatoma 7777 incorporated six times more label and those from hepatoma 7800 incorporated three times more label than Triton X-100-treated host liver nuclei. Nuclei from the three sources incorporated more label when exogenous DNA was added to the incubation system, but the difference in incorporation between the hepatoma nuclei and the host liver nuclei disappeared. When Triton X-100-treated nuclei, prepared from a tumor-bearing animal given injections of [3H]thymidine for 10 min were fractionated on sucrose gradients after disruption by high Mg2+ concentration, the fractions from hepatoma 7777 nuclei contained six times as much label as the host liver nuclear fractions. Nuclear fractions prepared from unabeled hepatomas or host livers had DNA polymerase activity. The activity, however, is the same in fractions prepared from hepatoma 7777 or host liver nuclei. It is suggested that the nuclear membrane does not play an important role in nuclear DNA synthesis. It is further suggested that the increased incorporation found with hepatoma nuclei is dependent on a physical or chemical arrangement of components within the nucleus and not solely on different enzyme levels.
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PMID:DNA synthesis in membrane-denuded nuclei and nuclear fractions from host liver and Morris hepatomas. 16 67

The high error rate characteristic of DNA polymerases from RNA tumor viruses has permitted measurements on the simultaneous incorporation of complementary and noncomplementary nucleotides during DNA synthesis. For example, avian myeloblastosis virus DNA polymerase incorporates 1 molecule of dCMP for approximately 500 molecules of dTMP polymerized using polyriboadenylic acid as a template. The parallel incorporation of complementary and noncomplementary nucleotides afer gel filtration of avian myeloblastosis virus DNA polymerase indicates that the observed fidelity is catalyzed by the polymerase itself. Nearest neighbor analysis of the product indicates that noncomplementary nucleotides are incorporated as single base substitutions. The incorporation of the noncomplementary dCMP is not reduced by a 20-fold greater amount of the complementary nucleotide, dTTP. Conversely, the concentration of the noncomplementary nucleotides does not effect the rate of incorporation of the complementary nucleotide. A similar lack of competition between complementary dGTP and noncomplementary dATP is exhibited using poly(rC)-oligo(dG) as a template-primer. Furthermore, there was no detectable competition between the different noncomplementary nucleotides. Possible explanations for this lack of competition are considered.
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PMID:Avian myeloblastosis virus DNA polymerase. Kinetic studies on the incorporation of noncomplementary nucleotides. 17 98

Primary mammary tumor cultures of RIII, GR, DD, BALB/c, and BALB/cfC3H mice were examined for mouse mammary tumor virus (MuMTV) production. Levels of production of 12-32 mug virus protein/day/75-cm2 culture flask could be maintained for 30-50 days with daily virus harvests. The viruses from tumor cell cultures of these mouse strains contained DNA polymerase with a strong preference for Mg++ over Mn++ as the divalent cation, a characteristic of DNA polymerase of MuMTV from mouse milk. These viruses from tumor cell cultures were excellent sources of MuMTV 3H-complementary DNA (complexed to 60-70S RNA) and radioactive 60-70S RNA, sufficiently free of contaminating murine leukemia virus nucleic acids, that can be used in molecular hybridization experiments. The effects of several culture parameters on MuMTV production were also studied.
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PMID:Characterization of mouse mammary tumor viruses from primary tumor cell cultures. II. Biochemical and biophysical studies. 17 74

Five different mouse mammary tumor cell lines were propagated in a serum free medium. Evaluation of growth characteristics, including logarithmic growth, cell population increase, protein production and days to confluency, showed serum-free medium comparable to serum-containing medium. Mouse mammary tumor virus expression and production, in C3H and GR tumor cell lines, as determined by virus particle counting and RNA dependent DNA polymerase assays, subsequent to dexamethasone stimulation revealed equivalent to higher levels of virus in serum-free medium as compared to serum-containing medium.
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PMID:Propagation of mouse mammary tumor cell lines and production of mouse mammary tumor virus in a serum-free medium. 18 96

Helenalin and tenulin injected into CF1 male mice bearing Ehrlich ascites tumors inhibit DNA synthesis and DNA polymerase enzymatic activity in the tumor cells. Helenalin inhibited protein synthesis. Both drugs increased the concentration of adenosine 3',5'-monophosphate, and interfered with glycolytic and mitochondrial energy processes. Cholesterol synthesis was also inhibited, resulting in lower serum cholesterol levels in tumor-bearing animals. Data obtained in vitro indicate that the cyclopentenone-bearing sesquiterpene lactone and related compounds do not alkylate puring bases of nucleic acids but rather undergo a Michael-type addition reaction with the sulfhydryl groups of reduced glutathione and l-cysteine. Thus, the inhibition of cellular enzyme activities and metabolism that has been observed with these drugs might be explained by the occurrence of a Michael-type teaction.
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PMID:Sesquiterpene antitumor agents: inhibitors of cellular metabolism. 19 9


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