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 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

A unique reaction for type II DNA topoisomerase is its cleavage of a pair of DNA strands in concert. We show however, that in a reaction mixture containing a molar excess of EDTA over Mg2+, or when Mg2+ is substituted by Ca2+, Mn2+, or Co2+, the enzyme cleaves only one rather than both strands. These results suggest that the divalent cations may play an important role in coordinating the two subunits of DNA topoisomerase II during the strand cleavage reaction. The single strand and the double strand cleavage reactions are similar in the following aspects: both require the addition of a protein denaturant, can be reversed by low temperature or high salt, and a topoisomerase II molecule is attached covalently to the 5' phosphoryl end of each broken DNA strand. Furthermore, the single strand cleavage sites share a similar sequence preference with double strand cleavage sites. There is, however, a strand bias for the single strand cleavage reaction. We show also that under single strand cleavage conditions, topoisomerase II still possesses a low level of double strand passage activity: it can introduce topological knots into both covalently closed or nicked DNA rings, and change the linking number of a plasmid DNA by steps of two. The implication of this observation on the sequential cleavage of the two strands of the DNA duplex during the normal DNA double strand passage process catalyzed by type II DNA topoisomerases is discussed.
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PMID:Single strand DNA cleavage reaction of duplex DNA by Drosophila topoisomerase II. 254 64

A type I topoisomerase has been purified from Diplococcus pneumoniae using phosphocellulose and hydroxylapatite chromatography. The purified enzyme catalyses the relaxation of negatively supercoiled DNA. The relaxation requires Mg2+ and is favoured by 0.2 M monovalent cations. The enzyme does not exhibit catenating or supercoiling activities. Using circular pBR322 DNA from dam+- and dam- -hosts as substrates for the enzyme, the relaxation reaction proceeds with somewhat higher efficiency with plasmids containing methylated adenine in GATC sequences. Plasmids from dcm+- and dcm- -hosts show no difference in reactivity.
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PMID:DNA topoisomerase I from Diplococcus pneumoniae. 254 82

RNA polymerase I preparations purified from a rat hepatoma contained DNA topoisomerase activity. The DNA topoisomerase associated with the polymerase had an Mr of 110,000, required Mg2+ but not ATP, and was recognized by anti-topoisomerase I antibodies. When added to RNA polymerase I preparations containing topoisomerase activity, anti-topoisomerase I antibodies were able to inhibit the DNA relaxing activity of the preparation as well as RNA synthesis in vitro. RNA polymerase II prepared by analogous procedures did not contain topoisomerase activity and was not recognized by the antibodies. The topoisomerase I: polymerase I complex was reversibly dissociated by column chromatography on Sephacryl S200 in the presence of 0.25 M (NH4)2SO4. Topoisomerase I was immunolocalized in the transcriptionally active ribosomal gene complex containing RNA polymerase I in situ. These data indicate that topoisomerase I and RNA polymerase I are tightly complexed both in vivo and in vitro, and suggest a role for DNA topoisomerase I in the transcription of ribosomal genes.
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PMID:Association of DNA topoisomerase I and RNA polymerase I: a possible role for topoisomerase I in ribosomal gene transcription. 285 18

A DNA helicase was extensively purified from Xenopus laevis ovaries. The most purified fraction was free of DNA topoisomerase, DNA polymerase, and nuclease activities. The enzyme had a Stokes radius of 54 A and a sedimentation coefficient of 6-7.3 S, from which a native molecular weight of 140,000-170,000 was calculated. DNA helicase activity required Mg2+ or Mn2+ and was dependent on hydrolysis of ATP or dATP. Monovalent cations, K+ and Na+, stimulated DNA unwinding with an optimum at 130 mM. DNA-dependent ATPase activity copurified with the X. laevis DNA helicase. Double-stranded and single-stranded DNA were both cofactors for the ATPase activity, but single-stranded DNA was more efficient. The molecular weight, monovalent cation dependence, cofactor requirements, and elution from single-stranded DNA-cellulose suggest that the X. laevis DNA helicase is different from previously described eukaryotic DNA helicases.
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PMID:A DNA helicase from Xenopus laevis ovaries. 285 68

Undiluted extracts from eggs or oocytes of Xenopus laevis support the assembly of chromatin with physiologically spaced nucleosomes. Micrococcal nuclease and DNase I digestion experiments show that nucleosome formation as well as supercoiling of circular DNA concomitant to assembly do not require ATP or Mg2+. However these factors are essential for the stability and the physiological spacing of the assembled chromatin. gamma-S-ATP can substitute for ATP in this process. With topoisomers of defined linking number topological interconversions proceed by steps of unity, both in vitro as well as in vivo, indicating that topoisomerase I is dominantly acting in this process. Novobiocin sensitivity occurred only with diluted extracts and was unrelated to an inhibition of topoisomerase II. Finally, nucleosome assembly occurs efficiently on linear DNA although the assembled DNA is less stable than with circular DNA. From these results we propose that mature chromatin is formed in a two-step reaction. In the first step, nucleosome deposition occurs independently of ATP and Mg2+. Thus, nucleosome formation can be uncoupled from their spacing. In this step, topoisomerase activity is involved in the relaxation of the topological constraints generated by chromatin assembly rather than in the process of assembly itself. The second step, requiring ATP and Mg2+, generates properly spaced chromatin.
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PMID:Assembly of spaced chromatin involvement of ATP and DNA topoisomerase activity. 285 62

DNA-dependent ATPase IV has been purified to near homogeneity from the Novikoff rat hepatoma. The enzyme is devoid of DNA polymerase, RNA polymerase, exonuclease, endonuclease, phosphomonoesterase, 3'- or 5'-phosphodiesterase, polynucleotide kinase, protein kinase, topoisomerase, helicase or DNA reannealing activities at a detection level of 10(-5) to 10(-7) relative to the ATPase activity. The enzyme is a monomer of Mr 110,000, has a sedimentation coefficient of 5.9 S, a Stokes radius of 40 A and a frictional coefficient of 1.32. In the presence of Mg2+ ion and a polynucleotide effector, ATPase IV hydrolyzes either ATP or dATP to the nucleoside diphosphate plus Pi. Other ribo- or deoxyribonucleoside triphosphates are not substrates. ATPase IV utilizes double-stranded DNA and single-stranded DNA as effector; however, it does not utilize poly(dT). The Km for dsDNA or ssDNA is 2.2 microM (nucleotide). A variety of ATP analogues were found to be competitive inhibitors of ATPase IV.
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PMID:Purification and enzymological characterization of DNA-dependent ATPase IV from the Novikoff hepatoma. 296 5

We have reported previously that rat liver mitochondria contain a topoisomerase and have shown it to be distinct from the nuclear enzyme by its sensitivity to Berenil and ethidium bromide. We report here some additional characterization. The enzyme differs further from its nuclear counterpart in its failure to bind to ssDNA cellulose and its chromatographic behavior on Sephadex; the latter procedure yields an Mr of 44 000 for the mitochondrial and 70 000 for the nuclear enzyme. The topoisomerase is strongly associated with mitochondrial membranes; only 10% of the activity could be extracted. The pH optimum of the enzyme falls between 6.0 and 8.5, with an NaCl optimum of 0.13 M in 0.1 M Tris (pH 8.3). Dithiothreitol is required, while N-ethylmaleimide is inhibitory. Tosylphenylalanine chloromethyl ketone, a serine proteinase inhibitor, abolishes activity; another, phenylmethanesulfonyl fluoride, has no effect. Berenil, a non-intercalating drug, and four of its analogues all inhibit with up to 100-fold differences in potency. No dependence on ATP, Mg2+, or both together could be shown. Neither novobiocin nor oxolinic acid shows any inhibitory effect. Nicked circles are generated in the presence of DMSO. These three observations are consistent with the topoisomerase being of the Type I class. Positively supercoiled pBR322 DNA, whose 6-8 positive turns were generated by altering solution conditions, is relaxed by the enzyme, indicating a lack of requirement for a negatively supercoiled substrate. We have also examined a partially purified preparation of the corresponding mitochondrial enzyme from mouse L cells. This enzyme is largely similar in properties to the rat liver enzyme. In isolated mitochondria, Berenil causes biphasic alterations in [3H]dATP incorporation into DNA, 10(-4) mM stimulating 2-fold, while higher concentrations inhibit. [3H]UTP incorporation into mitochondrial RNA also follows this pattern.
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PMID:Studies on mitochondrial type I topoisomerase and on its function. 298 52

In the absence of DNA aggregation, spermidine inhibited the relaxation of negatively supercoiled DNA by Escherichia coli topoisomerase I at concentrations of the polyamine normally found intracellularly. Spermidine also curtailed the cleavage of negatively supercoiled ColE1 DNA by the enzyme in the absence of Mg2+. On the contrary, knotting of M13 single-stranded DNA circles catalyzed by topoisomerase I was stimulated by the polyamine. Relaxation of supercoiled DNA by eukaryotic type 1 topoisomerases, such as calf thymus topoisomerase I and wheat germ topoisomerase, was significantly stimulated by spermidine in the same range of concentrations that inhibited the prokaryotic enzyme. In reactions catalyzed by S1 nuclease, the polyamine enhanced the digestion of single-stranded DNA and inhibited the nicking of negatively supercoiled DNA. These results suggest that spermidine modifies the supercoiled duplex substrate in these reactions by modulating the degree of single strandedness.
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PMID:Differential modulation by spermidine of reactions catalyzed by type 1 prokaryotic and eukaryotic topoisomerases. 300 Apr 18

The DNA topoisomerase I has been isolated from neurons of rat cerebral cortex. The most homogeneous fraction purified contains only one polypeptide of Mr approx. 100 000. The enzyme relaxes supercoiled DNA in the absence of ATP or Mg2+. The optimum monovalent cation concentration for the relaxation of superhelical DNA under conditions of DNA excess is found to be 175-200 mM. The neuron enzyme is similar to other mammalian type I DNA topoisomerases in that it links to the 3' ends of the broken DNA strands. Like calf thymus DNA topoisomerase I, the neuron topoisomerase can be selectively inhibited by poly(dG) but not by other homopolymerical deoxyribonucleotides.
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PMID:DNA topoisomerase I from rat brain neurons. 300 75


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