Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

SV40 chromatin can be isolated in two forms: At moderate ionic strength (mu = 0.1-0.3) it contains histone H1 in addition to the four nucleosomal histones and has a highly condensed appearance in the electron microscope, being composed of a few closely connected large spheres [190 A (160, 220) diameter]. At high ionic strength (mu = 0.6-0.8) or after prolonged exposure to very low ionic strengths (mu less than 0.02), the compact form unfolds and the chromatin shows a typical nucleosomal morphology. Native SV40 DNA-protein complexes contain a median number of 24 nucleosomes. The number of superhelical turns does not differ in DNA obtained from the compact and the unfolded forms of chromatin. DNA-relaxing enzyme is found associated with SV40 chromatin and is capable of acting both on extraneously added circular DNA and on its own DNA in the nucleoprotein complex. Purified DNA-relaxing enzyme forms transiently nicked DNA intermediates where the enzyme can be found covalently attached to the site of the nick in the DNA. Transcriptionally active SV40 complexes undergo the same ionic-strength-dependent structural transition as that of bulk SV40 chromatin and may therefore also have a compact configuration at physiological salt concentrations.
 ...
PMID:Biochemical and ultrastructural analysis of SV40 chromatin. 20 38

A DNA nicking-closing enzyme has been purified from the nuclei of mouse L cells to 90% homogeneity. The denatured and reduced form of the enzyme has a molecular weight of 68,000 which is in agreement with the molecular weight of the native enzyme as determined by gel filtration and by sucrose sedimentation velocity assuming the protein is globular. Therefore, the active form of the enzyme is a monopolypeptide. Its isoelectric point is pH 4.2 +/- 0.2. The nicking-closing activity does not require a cofactor and does not involve any sulfhydryl group. The enzyme requires 0.2 M NaCl and pH in the range of 6.5-7.5 for optimal activity.
 ...
PMID:Purification of a DNA nicking-closing enzyme from mouse L cells. 21 88

Extracts from Agrobacterium tumefaciens strain ID135 contain three enzymes that have been characterized and partially purified. The first enzyme, a DNA topoisomerase, appeared to relax only negatively twisted DNA. The second enzyme, Atu I, a type II restriction endonuclease, generated the identical DNA digestion pattern as EcoRII when several DNAs were used. The third enzyme, endonuclease A, showed a preference for superhelical DNAs as substrates. When plasmid pCK135DNA, obtained from the virulent strain IDI135 of A. tumefaciens, or plant DNA was exposed to the three enzymes, changes in DNA patterns were observed due to either conformational changes or digestion of the DNAs. These enzymes may function in vivo in the processing and incorporation of bacterial DNA in plant cells.
 ...
PMID:DNA modifying enzymes of Agrobacterium tumefaciens: effect of DNA topoisomerase, restriction endonuclease, and unique DNA endonuclease on plasmid and plant DNA. 21 32

A purified system is described for the introduction of negative supercoils into simian virus 40 DNA. The system consists of histones H2A, H2B, H3, and H4, DNA-relaxing enzyme, and a purified factor from Xenopus laevis stage 6 oocyte nuclei. The nuclei are prepared en masse by the technique of F. Scalenghe, M. Buscaglia, C. Steinheil, and M. Crippa [(1978) Chromosoma 60, 299-308]. The supercoiled simian virus 40 DNA prepared by this method is indistinguishable from simian virus 40 supercoiled DNA prepared from infected monkey cells.
 ...
PMID:DNA supercoiling by Xenopus laevis oocyte extracts: requirement for a nuclear factor. 21 4

The incubation of the E coli DNA binding protein HU with relaxed circular SV40 DNA in the presence of pure nicking-closing enzyme introduces up to 18 negative superhelical turns in the DNA molecules as measured by agarose gel electrophoresis. The maximal density of supercoiling is obtained at a HU-DNA mass ratio of 1. Reconstituted DNA-HU complexes prefixed with glutaraldehyde appear as condensed circular structures having an average of 14 "beads" per circular SV40 DNA molecule, with a "bead" diameter of 180 +/- 23 A. The circular SV40 DNA is condensed by a ratio of 2.0-2.5 relative to naked DNA. This is similar to the ratio (2.4) measured for chromatin formed by reassociation of relaxed SV40 DNA with the four core histones.
 ...
PMID:E. coli DNA binding protein HU forms nucleosomelike structure with circular double-stranded DNA. 22 78

A topoisomerase (nicking-closing enzyme) has been isolated from rat liver mitochondria. It has purified by double-stranded DNA-cellulose chromatography approximately 50,000-fold, based on the crude mitochondrial extract. It possesses a minimum specific activity of 1.9 x 10(5) units/mg. The enzyme has been shown to be distinctly mitochondrial, differentiated from the nuclear topoisomerase by its sensitivity to the intercalating drug, ethidium bromide, and to the non-intercalating trypanocidal drug, Berenil.
 ...
PMID:Mitochondria contain a distinct DNA topoisomerase. 22 16

A novel ATP-dependent DNA topoisomerase which makes reversible double-strand breaks in the DNA double helix has been purified to near homogeneity from T4 bacteriophage-infected Escherichia coli cells. Genetic data suggest that this activity is essential for initiating T4 DNA replication forks in vivo.
 ...
PMID:T4 DNA topoisomerase: a new ATP-dependent enzyme essential for initiation of T4 bacteriophage DNA replication. 22 89

Under some conditions, T4 DNA replication requires the products of the DNA-delay genes, genes 39, 52, 58, and 60. By using an in vitro complementation assay that stimulates DNA replication in T4 39(-)-infected cell extracts, T4 gene 39 protein has been purified. The purified fraction also contains complementing activities for T4 genes 52 and 60. On sodium dodecyl sulfate/polyacrylamide gel analysis the purified preparation exhibits three protein components: a 51,000-dalton protein corresponding to the product of gene 52, a 64,000-dalton protein corresponding to the product of gene 39, and a 110,000-dalton protein. This purified fraction shows a DNA topoisomerase activity that untwists superhelical DNA in an ATP- and Mg2+-dependent reaction. The analogs adenylyl imidodiphosphate and adenyl [beta, gamma-methylene]diphosphonate cannot be used to replace ATP. The topoisomerase activity is not sensitive to the antibiotics oxolinic acid and novobiocin, known antagonists of Escherichia coli DNA gyrase. The possible relationship among the three polypeptides and their biological activities is discussed.
 ...
PMID:T4 DNA-delay proteins, required for specific DNA replication, form a complex that has ATP-dependent DNA topoisomerase activity. 22 76

The four core histones (H2A, H2B, H3, and H4) and DNA were assembled into nucleosome-like particles at physiological ionic strengths either by an extract of chromatin rich in nicking-closing activity or by the purified nicking-closing enzyme itself. When histone-DNA complexes were assembled in vitro from relaxed circular DNA, nearly physiological numbers of superhelical turns were induced in the DNA molecule. Electron microscopy of the complexes assembled by the chromatin extract revealed a beaded structure and a reduction of the contour length compared to free DNA. Micrococcal nuclease digestion of the histone-DNA complexes yielded 145-base-pair DNA fragments typical of nucleosome core particles and shorter subnucleosomal DNA fragments of discrete length.
 ...
PMID:Nicking-closing enzyme assembles nucleosome-like structures in vitro. 22 80

A DNA-relaxing enzyme capable of concerted nicking and closing of DNA backbone bonds has been purified from Haemophilus gallinarum by two chromatographic steps and gel filtration. The enzyme efficiently catalyzes the removal of superhelical turns from a negatively twisted DNA and requires Mg2+ for this activity. Slight removal of superhelical turns from a positively twisted DNA generated by binding of ethidium bromide is found, but only at high enzyme concentrations. The DNA-relaxing activity is inhibited markedly with heat-denatured DNA, whereas native DNA and RNA have almost no affect on this activity.
 ...
PMID:Purification and characterization of DNA-relaxing enzyme from Haemophilus gallinarium. 22 61


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>