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:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The virD locus of Agrobacterium tumefaciens Ti plasmid encodes functions necessary for endonucleolytic cleavage of transferred DNA (T-DNA) prior to its transfer to plant cells. For the overproduction of the VIRD proteins in Escherichia coli a tac-virD operon fusion was constructed. A significant increase in the accumulation of VIRD proteins was observed in a lon protease-deficient E. coli host. The presence of an overlapping open reading frame (ORF) upstream of the VIRD1 coding sequence had a negative effect on VIRD1 production. A preparation containing VIRD proteins catalyzes the conversion of supercoiled (form I) DNA to relaxed (form IV) DNA. This activity is similar to that of a DNA topoisomerase. The relaxation activity lacks DNA sequence specificity, requires magnesium ion, and has no requirement for an energy source. Studies with plasmids that had lost defined DNA segments encompassing various virD coding regions showed that VIRD1 is the DNA-relaxing enzyme. In a density gradient centrifugation experiment, the DNA-relaxing activity sedimented as a 21-kDa polypeptide. Earlier studies of Jayaswal et al. [Jayaswal, R., Veluthambi, K., Gelvin, S. & Slightom, J. (1987) (J. Bacteriol. 169, 5035-5045] have shown that in E. coli VIRD2 alone is not sufficient for endonucleolytic cleavage of T-DNA and requires VIRD1 for its activity.
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PMID:The virD operon of Agrobacterium tumefaciens Ti plasmid encodes a DNA-relaxing enzyme. 254 31

We have isolated DNA polymerases and topoisomerases from two thermoacidophilic archaebacteria: Sulfolobus acidocaldarius and Thermoplasma acidophilum. The DNA polymerases are composed of a single polypeptide with molecular masses of 100 and 85 kDa, respectively. Antibodies against Sulfolobus DNA polymerase did not cross react with Thermoplasma DNA polymerase. Whereas the major DNA topoisomerase activity in S. acidocaldarius is an ATP-dependent type I DNA topoisomerase with a reverse gyrase activity, the major DNA topoisomerase activity in T. acidophilum is a ATP-independent relaxing activity. Both enzymes resemble more the eubacterial than the eukaryotic type I DNA topoisomerase. We have found that small plasmids from halobacteria are negatively supercoiled and that DNA topoisomerase II inhibitors modify their topology. This suggests the existence of an archaebacterial type II DNA topoisomerase related to its eubacterial and eukaryotic counterparts. As in eubacteria, novobiocin induces positive supercoiling of halobacterial plasmids, indicating the absence of a eukaryotic-like type I DNA topoisomerase that relaxes positive superturns.
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PMID:Studies on DNA polymerases and topoisomerases in archaebacteria. 254 77

Extensive digestion of the covalent intermediate between DNA and Saccharomyces cerevisiae DNA topoisomerase I with trypsin yields a 7-amino acid peptide covalently linked to DNA. Direct sequencing of the DNA-linked peptide identifies Tyr-727 as the active site tyrosine that forms an O4-phosphotyrosine bond with DNA when the enzyme cleaves a DNA phosphodiester bond. Site-directed mutagenesis of the cloned yeast TOP1 gene encoding the enzyme confirms the essentiality of Tyr-727 for the relaxation of supercoiled DNA by the enzyme. From amino acid sequence homology, Tyr-771 and -773 are readily identified as the active site tyrosines of Schizosaccharomyces pombe and human DNA topoisomerase I, respectively. Sequence comparison and site-directed mutagenesis also implicate Tyr-274 of vaccinia virus DNA topoisomerase as the active site residue. There appears to be a 70-amino acid domain near the carboxyl terminus of eukaryotic DNA topoisomerase I and vaccinia topoisomerase, within which the active site tyrosine resides.
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PMID:Peptide sequencing and site-directed mutagenesis identify tyrosine-727 as the active site tyrosine of Saccharomyces cerevisiae DNA topoisomerase I. 254 38

In a yeast DNA topoisomerase double mutant TG205 (delta top1 top2-4), over half of the rDNA is present as extrachromosomal rings containing one 9 kb unit of the rDNA gene or tandem repeats of it. Expression of a plasmid-borne TOP1 or TOP2 gene in the strain leads to the integation of the extrachromosomal rDNA rings back into the chromosomal rDNA cluster. When the plasmid-borne topoisomerase gene is expressed from an inducible promoter of the GAL1 gene, repression of the gene by dextrose leads to reappearance of the extrachromosomal rDNA rings. The DNA topoisomerase-dependent excision/integration of rDNA is discussed in terms of the possibility of rDNA supercoiling by transcription and the effects of DNA topology on intra- and interchromosomal recombination.
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PMID:A subthreshold level of DNA topoisomerases leads to the excision of yeast rDNA as extrachromosomal rings. 254 96

The DNA endonuclease (Aendo) and DNA topoisomerase (Atopo) activities in liver nucleus extracts of normal rats, in DENA-induced hepatomas and in liver tissues around tumours were investigated. The profile of nuclear endonucleases measured in the presence of 2 mM CaCl2 + 5 mM MgCl2, or 5 mM MnCl2, or 5 mM MgCl2, or 2 mM CaCl2 (pH 7.4), or I mM EDTA (pH 5.0) was different in normal and tumour tissues. Mn2+-dependent endonuclease was the main endonuclease in the tumour tissue, whereas Ca2+, Mg2+-dependent endonuclease was the main one in the normal liver and in the tissue around the tumour. An increase in the Mn2+-dependent endonuclease activity correlated with a decrease in the hepatoma differentiation level. Atopo of types I and II increased in the tissue around the tumour. Aendo and Atopo of cellular nuclei decreased in animals given DENA without the liver tumour.
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PMID:[The activity of nuclear endonucleases and topoisomerases in the liver of rats and in diethylnitrosamine-induced tumors]. 254 92

We have previously shown that purified T4 DNA topoisomerase promotes illegitimate recombination between two lambda DNA molecules, or between lambda and plasmid DNA in vitro (Ikeda, H. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 922-926). Since the recombinant DNA contains a duplication or deletion, it is inferred that the cross-overs take place between nonhomologous sequences of lambda DNA. In this paper, we have examined the sequences of the recombination junctions produced by the recombination between two lambda DNA molecules mediated by T4 DNA topoisomerase. We have shown that there is either no homology or there are 1-5-base pair homologies between the parental DNAs in seven combinations of lambda recombination sites, indicating that homology is not essential for the recombination. Next, we have shown an association of the recombination sites with the topoisomerase cleavage sites, indicating that a capacity of the topoisomerase to make a transient double-stranded break in DNA plays a role in the illegitimate recombination. A consensus sequence for T4 topoisomerase cleavage sites, RNAY decreases NNNNRTNY, was deduced. The cleavage experiment showed that T4 topoisomerase-mediated cleavage takes place in a 4-base pair staggered fashion and produces 5'-protruding ends.
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PMID:Common sites for recombination and cleavage mediated by bacteriophage T4 DNA topoisomerase in vitro. 254 34

A series of analogues of etoposide, the C-4 amino- and alkylamino-substituted 4'-demethyl-epipodophyllotoxins, have been synthesized and studied for their activity to inhibit type II human DNA topoisomerase as well as their activity in causing cellular protein-linked DNA breakage. Substitution of the glycosidic moiety of 1 by a 2"-hydroxyethylamino or 2"-methoxyethylamino chain at the C-4 beta position resulted in potent inhibitors of the human DNA topoisomerase II. This inhibitory activity correlates reasonably well with their activity in causing protein-linked DNA breakage in KB cells. The in vitro cytotoxicity (KB) appears to have no correlation with the inhibitory activity of the human DNA topoisomerase II.
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PMID:Antitumor agents, 107. New cytotoxic 4-alkylamino analogues of 4'-demethyl-epipodophyllotoxin as inhibitors of human DNA topoisomerase II. 255 May 87

Incubation of cultured rat aortic smooth muscle cells (A-10, ATCC CRL 1476) with [8-arginine]vasopressin (AVP) or thrombin increased the amount of DNA strand breakage induced by camptothecin, an inhibitor of topoisomerase I (DNA topoisomerase; EC 5.99.1.2) and transiently stimulated the extractable activity of this enzyme. Both topoisomerase-related responses were prevented by treatment of the cells with AVP or thrombin plus the appropriate receptor antagonist. The increase in strand breakage mediated by AVP and thrombin depended on the concentration of hormone. Neither AVP nor thrombin had any effect on strand breaks obtained with the epipodophyllotoxin VM-26, an inhibitor of topoisomerase II [DNA topoisomerase (ATP-hydrolysing); EC 5.99.1.3]. Pretreatment of the cells with pertussis toxin partially inhibited thrombin-mediated increases in camptothecin-induced strand breakage whereas AVP-mediated increases were unaffected. These results are consistent with the notion that AVP and thrombin induce a transient increase in intracellular topoisomerase I activity via interactions with their respective cell surface receptors and that the effects of the activation of these receptors are mediated by different G-proteins.
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PMID:Stimulation of intracellular topoisomerase I activity by vasopressin and thrombin. Differential regulation by pertussis toxin. 255 99

DNA topoisomerase activity can be rapidly assayed by measuring the change in ethidium bromide fluorescence intensity after treatment of closed duplex DNA with enzyme. The sensitivity of the fluorometric assay has been enhanced 3-fold by a 10-fold reduction in ethidium bromide concentration to 0.1 microgram/ml. The results of the fluorometric assays are in close agreement with agarose gel electrophoretic analyses of reacted DNA. A sensitive fluorometric method using 0.1 microgram/ml ethidium bromide has also been developed to determine the fraction of nicked and linear DNAs in a mixture containing closed duplex DNA by measuring the fluorescence intensities of ethidium-DNA complexes at pH 7.0 and pH 12.0. These methods make possible very rapid and sensitive measurements of DNA topoisomerase and endonuclease activities.
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PMID:Fluorometric methods employing low concentrations of ethidium bromide for DNA topoisomerase and endonuclease assays. 255 90

DNA topoisomerase type I and II activities were determined by serial dilution in nuclear extracts from control and ataxia-telangiectasia lymphoblastoid cells. Topoisomerase I activity, assayed by relaxation of supercoiled plasmid DNA, was found to be approximately the same in both cell types. In order to remove interference from topoisomerase I, the activity of topoisomerase II was measured by the unknotting of knotted P4 phage DNA in the presence of ATP. The activity of topoisomerase II was markedly reduced in two ataxia-telangiectasia cell lines, AT2ABR and AT8ABR, compared to controls. This reduction in activity was detected with increasing concentration of protein and in time course experiments at a single protein concentration. A third cell line, AT3ABR, did not have a detectably lower activity of topoisomerase II when assayed under these conditions. The difference in topoisomerase II activity in the ataxia-telangiectasia cell lines examined may reflect to some extent the heterogeneity observed in this syndrome.
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PMID:A defect in DNA topoisomerase II activity in ataxia-telangiectasia cells. 282


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