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:5.99.1.3 (topoisomerase)
9,911 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

At concentrations normally used to inhibit eukaryotic type II topoisomerase activity (100-1000 micrograms/ml) novobiocin binds core histones. Approximately 15 moles of novobiocin bind per mole of histone resulting in histone precipitation from solution in either 0.15 M or 2 M NaCl. The interaction between novobiocin and proteins appears to involve arginine residues: histones H3 and H4 (13.5 and 14 mole percent arginine) are precipitated at lower novobiocin concentrations than histones H2A and H2B (9.5 and 6.5 mole percent arginine). Furthermore, polyarginine but not polyornithine competes for novobiocin in histone precipitation. Moreover, histones with arginine residues modified with 1,2-cyclohexanedione are soluble in 1000 micrograms/ml novobiocin. Because novobiocin can remove histones from solution as well as inhibit topoisomerase activity, and because both of these events can alter DNA topology, novobiocin should be used with caution in experiments designed to implicate topoisomerase activity in chromatin dynamics.
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PMID:Novobiocin precipitates histones at concentrations normally used to inhibit eukaryotic type II topoisomerase. 371 93

Inhibitors of DNA polymerase alpha (aphidicolin, phosphonoacetic acid, phosphonoformic acid) efficiently inhibit initiator-induced amplification of SV40 DNA sequences in the SV40-transformed Chinese hamster cell line CO631. Amplification is also inhibited by various protease inhibitors (antipain, leupeptin, aprotinin, alpha-I-antitrypsin, epsilon-amino-caproic acid, soy-bean protease inhibitor), by the non-initiating but DNA-damaging agent caffeine, and by sodium butyrate, which inhibits DNA synthesis by histone modification. In contrast, an inhibitor of topoisomerase II, nalidixic acid, enhances amplification when applied simultaneously with initiating treatment. This latter compound does not induce amplification when applied without initiator. Cycloheximide induces DNA amplification in the same way as chemical and physical carcinogens. This amplification can still be observed when protein synthesis is completely blocked. The data suggest a complex mechanism of selective DNA amplification. The possible involvement of proteases leading to a functional modification of DNA polymerase alpha is discussed.
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PMID:Selective DNA-amplification induced by carcinogens (initiators): evidence for a role of proteases and DNA polymerase alpha. 389 46

4'-(9-Acridinylamino)methanesulfon-m-anisidide (m-AMSA) and other DNA intercalating agents produce protein-associated DNA strand breaks, the formation of which are mediated by topoisomerase-like chromosomal proteins. As topoisomerases would be expected to be most active during DNA replication, DNA synthesis inhibitors may alter the sensitivity of cellular DNA to intercalator-induced scission. We report that treatment of L1210 cells with 1-beta-D-arabinofuranosylcytosine (ara-C) (0.1 microM) or hydroxyurea (HU) (0.1 mM) for 18 hr resulted in a 2- to 2.4-fold enhancement of m-AMSA-induced protein-associated DNA single-strand breaks and DNA-protein cross-links as measured by alkaline elution. This enhancement was dependent on the duration of ara-C or HU treatment as well as on the concentration of ara-C or HU. Enhancement did not correlate with any alteration in cellular uptake of intercalator or with ara-C- or HU-induced alterations in the DNA synthetic rate. The DNA within nuclei isolated from ara-C- or HU-treated cells also displayed an enhanced susceptibility to m-AMSA-induced scission. There was a correlation between enhanced single-strand break formation and recruitment of cells into S-phase as well as between single-strand break formation and the production of a hypomethylated state of cellular DNA. Concurrent with the enhancement of m-AMSA-induced cellular DNA effects was a synergistic effect on m-AMSA cytotoxicity by ara-C or HU. This enhancement of intercalator effects was also found for the intercalator Adriamycin. We propose that these sublethal concentrations of ara-C and HU alter chromatin structure possibly via DNA hypomethylation and/or altered DNA-histone interactions so that intercalator-induced DNA effects are enhanced. Alternatively, the topoisomerase-like activity involved in intercalator-induced, protein-associated DNA break production may be increased in the nuclei of ara-C- or HU-treated cells.
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PMID:Enhancement of the DNA breakage and cytotoxic effects of intercalating agents by treatment with sublethal doses of 1-beta-D-arabinofuranosylcytosine or hydroxyurea in L1210 cells. 620 99

The lower eukaryote Ustilago maydis contains a topoisomerase that removes supercoils from negative and positive superhelical DNA. The enzyme may be a multimeric protein or an aggregate of polypeptides with a native molecular weight of 270,000 as estimated by gel filtration. No cofactors are required by the enzyme, but activity is enhanced by Mg2+. Dependence of activity upon enzyme concentration is not linear. Below a threshold level where topoisomerase cannot ordinarily be detected, addition of H1 histone sharply stimulates activity. ATP and a number of structural analogues inhibit the enzyme.
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PMID:Purification and properties of a topoisomerase from Ustilago maydis. 627 Jan 8

A simple method for the purification of the major topoisomerase (topoisomerase 1) from chicken erythrocytes is described. Because of the generally repressed state of the chromatin from these nuclei, the heterogeneity of the non-histone proteins is reduced, and it is possible to purify this enzyme from a nuclear extract by a single chromatographic step. The chicken erythrocyte topoisomerase appears to be similar to previously described eukaryotic type I topoisomerases with respect to its physical and enzymological properties. The pattern of intermediate products generated during the action of chicken erythrocyte topoisomerase on a supercoiled closed circular DNA substrate has been examined quantitatively and has been shown to be consistent with a mechanism in which the enzyme closes its substrate DNA molecular after the removal of each superhelical turn and in which dissociation of the enzyme substrate complex may, but does not necessarily, occur after each cycle of the reaction.
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PMID:Purification and properties of type 1 topoisomerase from chicken erythrocytes: mechanism of eukaryotic topoisomerase action. 628 Jul 58

We have examined the ability of a topoisomerase purified from chicken erythrocyte nuclei to mediate nucleosome core assembly in vitro at physiological ionic strength (0.15 M NaCl). Although we have detected limited amounts of spontaneously assembled nucleosome cores at this salt concentration, the addition of this topoisomerase does not increase the amount of assembly observed. Nucleosome assembly was assayed by quantitating the amount of core particle length DNA accumulated with time upon the nuclease digestion of histone-DNA complexes. In addition, the amount of negative supercoils introduced into relaxed closed circular DNA upon nucleosome core particle assembly was determined. Correctly assembled complexes do not protect more DNA from nuclease digestion than random histone-DNA complexes but shift the heterogeneous size distribution of protected fragments to a more homogeneous distribution centred around 145 base pairs. Under our conditions of nucleosome assembly, a second histone-DNA complex which is distinct from the nucleosome core can be detected under physiological ionic strength conditions. This particle does not form in high salt assembly experiments. Similarly, the assembly of this particle is unaffected by the presence or absence of topoisomerase.
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PMID:A topoisomerase from chicken erythrocyte nuclei which does not assemble nucleosome core particles in vitro. 628 3

A histone-like protein (H) from Escherichia coli has been purified to more than 98% homogeneity by using its capacity to inhibit DNA functions. H protein behaves as a dimer of 28,000-dalton subunits. The histone H2A-like properties of H protein are: (i) binding to DNA at a stoichiometry of 1 H protein dimer per 75 bases; (ii) abundance of about 30,000 molecules per cell, sufficient to bind about 20% of the chromosome; (iii) limiting digestion of double-stranded DNA by micrococcal nuclease; (iv) reannealing of complementary single-stranded DNA; (v) amino acid composition resembling that of eukaryotic histone H2A; (vi) neutralization of H protein by antibody specific for H2A; (vii) heat stability; and (viii) acid solubility. The capacity of H protein to bind DNA prevents its template or substrate functions n several reactions in vitro: DNA synthesis by several polymerases; transcription by RNA polymerase; DNA topoisomerase activity; and DNA-dependent ATP hydrolysis by rep protein, dnaB protein, or protein n'. Together with other histone-like proteins of E. coli, H protein may organize the E. coli chromosome into nucleosomes, such as in eukaryotic chromatin.
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PMID:Novel histone H2A-like protein of escherichia coli. 700 71

We have analysed the unwinding of nucleosomally organized DNA by simian virus 40 large tumour (T) antigen. Isolated T antigen can bind to existing nucleosome cores containing the viral replication origin sequence, which results in displacement of the histone octamer and unwinding of the DNA. However, specific binding to nucleosome cores is salt sensitive and nearly completely blocked under ionic conditions that otherwise support DNA replication. Once started, the progressing T antigen helicase, like an elongating RNA polymerase, is not further repressed by histone octamers, irrespective of the presence or absence of linker histone H1. Disruption of the nucleosomal structure in the process of unwinding may be assisted by the demonstrated interaction of the hexameric T antigen complex with histone proteins H1 and H3. Finally, our studies reveal the inability of topoisomerase I and/or II to continually relieve the superhelical tension of covalently closed circular minichromosomes as generated during their unwinding by T antigen. This may indicate that chromatin relaxation during the process of DNA replication can only be efficiently performed by a topoisomerase that is (trans)activated by other factors.
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PMID:Unwinding of chromatin by the SV40 large T antigen DNA helicase. 762 34

We have determined that the major mitotic phosphoprotein in chromosomes recognized by the antiphosphoprotein antibody MPM-2 is the 170-kDa isoform of topoisomerase II (topo II), the isoform predominant in proliferating cells. As a prerequisite to making this discovery, it was necessary to develop protocols to protect chromosomal proteins from dephosphorylation during cell extraction and chromosome isolation procedures. Immunofluorescence analysis of the large chromosomes prepared from Indian Muntjac cells revealed colocalization of MPM-2 and anti-topo II antibodies to the chromosomal centromeres and to the axial regions of the chromosomal arms. For biochemical fractionation studies, large quantities of chromosomes from the P388D1 mouse lymphocyte cell line were isolated and treated to remove DNA and histone proteins. Immunoblot and immunoprecipitation experiments with this chromosome scaffold fraction identified the major MPM-2-reactive phosphoprotein to be DNA topo II. Using a panel of anti-peptide antibodies specific to the isoforms of topo II, we determined that the major phosphoprotein recognized by MPM-2 is the 170-kDa isoform of topo II, topo II alpha. The 180-kDa isoform, topo II beta, present in the isolated chromosomes in much smaller quantities, is also recognized by MPM-2. The mitotic phosphorylation of the topo II proteins may be critical for proper chromosome condensation and segregation.
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PMID:DNA topoisomerase II alpha is the major chromosome protein recognized by the mitotic phosphoprotein antibody MPM-2. 769 Sep 61

Mammalian spermiogenesis is marked by the initial disruption of the nuclear-histone-DNA complex by the transition proteins for ultimate replacement with protamines. The genes for three of these low molecular weight basic nuclear proteins exist as a single linear array of PRM1, PRM2, and TNP2 on human chromosome 16p13.2. To begin to address the mechanism governing their transcriptional potentiation, a region of approximately 40 kilo-bases of the human genome encompassing these genes was introduced into the germ line of mice. Fluorescence in situ hybridization and Southern analysis showed that this segment of the human genome integrated into independent chromosomal sites while maintaining its fidelity. Transcript analysis demonstrated that the expression of the endogenous mouse protamine Prm1 and Prm2 genes as well as the mouse transition protein Tnp2 gene were expressed along with their human transgene counterparts. The pattern of expression of these transgenic human genes within this multigenic cluster faithfully represented that observed in vivo. In addition, all members of this transgenic gene cluster were expressed in proportions similar to those in human testis. Copy number-dependent and position-independent expression of the transgenic construct demonstrated that the corresponding biological locus was contained within this segment of the human genome. Furthermore, DNase I sensitivity established that in sperm the human PRM1-->PRM2-->TNP2 genic domain was contained as an approximately 28.5-kilobase contiguous segment bounded by an array of nuclear matrix associated topoisomerase II consensus sites. This is the first description of a multigenic male gamete-specific domain as a fundamental gene regulatory unit. A model of haploid-specific gene determination is presented.
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PMID:A haploid expressed gene cluster exists as a single chromatin domain in human sperm. 772 81


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