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)

Closed-circular, superhelical DNA from simian virus 40 (SV40 DNA I) was treated with an excess of DNA-relaxing enzyme in the presence of increasing amounts of ethidium bromide (EtdBr). After removal of the ethidium, each sample consisted of a group of close-circular DNA molecules differing in their number of superhelical turns (tau) around a mean value of tau in a Gaussian-like distribution. The DNA samples were analyzed by electrophoresis in agarose gels under conditions where the electrophoretic mobility was a function of the number of superhelical turns. Since the distributions around tau of DNA molecules of different samples overlappped, the difference in the mean number of superhelical turns from sample to sample, delta tau, could be determined and used to measure the mean number (tau) for native SV40 DNA I. By this criterion, SV40 DNA I contains a Gaussian-like distribution of molecules differing by integral numbers around a mean value of tau = -24 +/- 2 at 37 degree C [in 0.2 M NaC1, 10 mM Tris-HC1 (pH 7.9), and 0.2 mM EDTA]. The heterogeneity in tau is probably a consequence of thermal fluctuations in the DNA helix at the time when the last phospholiester bond is closed in vivo. When correlated to the buoyant shift of completely relaxed SV40 DNA in a CsC1-propidium diiodide gradient, the number of delta tau = 24 +/- 2 of superhelical versus relaxed DNA implies an unwinding of the DNA helix by 26-28 degree upon intercalation of one molecule of EtdBr.
Proc Natl Acad Sci U S A 1975 Dec
PMID:Determination of the number of superhelical turns in simian virus 40 DNA by gel electrophoresis. 17 79

A DNA-relaxing enzyme which catalyzes the conversion of superhelical DNA to a non-superhelical covalently closed form has been purified from Micrococcus luteus to near homogeneity by two chromatographic steps. The enzyme is a single polypeptide chain. As determined by sodium dodecyl sulfate - polyacrylamide gel electrophoresis and gel filtration on Sephadex G 150, the molecular weight is 115,000. The DNA-relaxing activity determined as a function of enzyme concentration follows a sigmoidal curve. The enzyme requires Mg++ for activity. In the presence of 4.5 mM Mg++ addition of 50-250 mM KCl yields incompletely relaxed DNA molecules (intermediates); intermediates are also observed in the absence of KCl, when the reaction is carried out at 0 degree C or at Mg++ concentrations exceeding 10 mM.
Nucleic Acids Res 1977 Dec
PMID:DNA-relaxing enzyme from Micrococcus luteus. 20 27

Renaturation of two complementary single-stranded circles should be limited by topological constraints against the rewinding of the DNA helix. If a mixture of complementary single-stranded rings is annealed and then treated with the DNA untwisting enzyme, the DNA circles completely renature as judged by (i) the presence of interlocked rings that sediment at 53 S in alkali, (ii) the buoyant density of the renatured DNA in CsCl gradients containing ethidium bromide, and (iii) the resistance of the product to the single-strand-specific S1 nuclease. Therefore, the DNA untwisting enzyme is able to provide a transient single-strand break that is sufficient to allow the two strands to completely rewind. The possibility that the untwisting enzyme might facilitate the initiation of the process of genetic recombination is discussed.
Proc Natl Acad Sci U S A 1977 Dec
PMID:Renaturation of complementary single-stranded DNA circles: complete rewinding facilitated by the DNA untwisting enzyme. 20 51

We have identified a topoisomerase activity from Escherichia coli related to DNA gyrase (topoisomerase II): we designate it topoisomerase II'. It was constructed of two subunits, which were purified separately. One is the product of the gyrA (formerly nalA) gene and is identical to subunit A of DNA gyrase. The other is a 50,000-dalton protein, which we have purified to homogeneity and call v. v may be a processed form of the much larger gyrase subunit B or may be derived from a transcript of part of the subunit B structural gene, because preliminary peptide maps of the two subunits are similar. Topoisomerase II' relaxes negatively supercoiled DNA and, uniquely among E. coli topoisomerases, relaxes positive supercoils efficiently. It is the only topoisomerase that can introduce positive supercoils; these are stoichiometric with enzyme molecules. Topoisomerase II' resembles gyrase in its sensitivity to oxolinic acid, the wrapping of DNA in an apparent positive supercoil around the enzyme, and the introduction in an aborted reaction of site-specific double-strand breaks in the DNA with concomitant covalent attachment of protein to both newly created 5' ends. Unlike DNA gyrase, topoisomerase II' has no negative supercoiling activity. Functional chimeric topoisomerases were constructed with the alpha subunit of the Micrococcus luteus gyrase and v or gyrase subunit B from E. coli. We discuss the implications of the dual of the gyrA gene product.
Proc Natl Acad Sci U S A 1979 Dec
PMID:A topoisomerase from Escherichia coli related to DNA gyrase. 23 Apr 98

The interaction of closed circular duplex DNA with the lysine-rich H5 histone fraction of avian erythrocytes has been studied. H5, like H1 histone, interacts preferentially with superhelical DNA. The extent of interaction increases with increasing negative or positive superhelicity. Salt-extracted lysine-rich histones show the same specificity for interaction with superhelices as do acid-extracted preparations. Chicken erythrocyte nuclei contain DNA-relaxing enzyme. This enzyme is extracted from the nuclei at lower salt concentrations than those required to extract H1 and H5 histones and is, therefore, probably a function of a protein distinct from H1 and H5 histones.
J Biol Chem 1976 Dec 10
PMID:H5 Histone and DNA-relaxing enzyme of chicken erythrocytes. Interaction with superhelical DNA. 100 94

In fungi, most mitotic recombination and at least some meiotic recombination appear to stem from a process of double-strand break repair. During this repair, recombination occurs by conversion caused by the process of double-strand gap filling, by conversion related to heteroduplex formation where homologous molecules interact by complementary base pairing, and by crossing-over which is probably an occasional byproduct of the repair process. From a review of the genetic and biochemical data and the published models of the process of recombination, the following view emerges: broken ends may be acted upon by nucleases and helicases to produce a recombinagenic end which may have both 3' and 5' single-stranded tails. These postulated split-ends may then act independently to find regions of homology with which to react. Invasion by both ends forms two splice-junctions which prime DNA synthesis towards each other to replace lost information, using the homologous sequences as templates. This process would lead to a structure which consists of a double Holliday junction which may be resolved endonucleolytically, sometimes giving a crossover, or by another means such as the action of topoisomerase, to dissolve the structure without a crossover having been formed.
Mutat Res 1992 Dec 01
PMID:Mechanism and control of recombination in fungi. 127 96

Certain 2-substituted 1H-pyrrolo [3,2-h] quinolines have been prepared and their biological activity in mammalian cells and in some microorganisms have been studied. These compounds represent a simplified ellipticine heterocyclic moiety: in addition they have a different ring condensation, leading to an angular molecular structure instead of a linear one. In mammalian cells all compounds appeared to be able of inducing an antiproliferative effect and an extensive DNA fragmentation, similarly to ellipticine, even if to a reduced extent. The new derivatives behaved in a comparable way also on some microorganisms, such as T2 bacteriophage (which appears to be less sensitive than mammalian cells) and in mutagenesis tests carried out with E. coli WP2 TM9 and S. typhimurium TA 98, which are reverted by base substitution and frame-shift mutagens, respectively. Similarly to the reference compound, all ellipticine analogues appeared to be no mutagenic. The obtained results suggest that they induce the antiproliferative activity in mammalian cells mainly as topoisomerase inhibitors, similarly to ellipticine itself. Therefore, they represent an interesting model to design new potential anticancer drugs.
Farmaco 1992 Dec
PMID:2-substituted 1H-pyrrolo [3,2-h] quinoline derivatives: synthesis and aspects of their biological activity. 129 67

DNA topoisomerases have been shown to be important therapeutic targets in cancer chemotherapy. We found that KT6006 and KT6528, synthetic antitumor derivatives of indolocarbazole antibiotic K252a, were potent inducers of a cleavable complex with topoisomerase I. In DNA cleavage assay using purified calf thymus DNA topoisomerase I and supercoiled pBR322 DNA, KT6006 induced topoisomerase I mediated DNA cleavage in a dose-dependent manner at drug concentrations up to 50 microM, while DNA cleavage induced by KT6528 was saturated at 5 microM. The maximal amount of nicked DNA produced by KT6006 was more than 50% of substrate DNA, which was comparable to that of camptothecin. Heat treatment (65 degrees C) of the reaction mixture containing these compounds and topoisomerase I resulted in a substantial reduction in DNA cleavage, suggesting that topoisomerase I mediated DNA cleavage induced by KT6006 and KT6528 is through the mechanism of stabilizing the reversible enzyme-DNA "cleavable complex". Both KT6006 and KT6528 did not induce topoisomerase II mediated DNA cleavage in vitro. KT6006 and KT6528 were found to induce nearly identical topoisomerase I mediated DNA cleavage patterns, which was distinctly different from that with camptothecin. In contrast to the similarity between KT6006 and KT6528 in their structures and the nature of their cleavable complex with topoisomerase I, these drugs have different properties with respect to their interaction with DNA: KT6006 is a very weak intercalator whereas KT6528 is a strong intercalator with potentials comparable to that of adriamycin. These results indicate that KT6006 and KT6528 represent a new distinct class of mammalian DNA topoisomerase I active antitumor drugs.
Biochemistry 1992 Dec 08
PMID:Induction of mammalian DNA topoisomerase I mediated DNA cleavage by antitumor indolocarbazole derivatives. 133 91

A previous report from this laboratory demonstrated that novobiocin produced supra-additive cytotoxicity when combined with etoposide (VP-16) or teniposide (VM-26) in WEHI-3B D+ and A549 cells. The increase in cytotoxicity was accompanied by an increase in the formation of drug-stabilized protein-DNA covalent complexes. We now report that novobiocin increased the amount of VP-16-induced covalent complexes between the 170 kDa form of topoisomerase II and DNA in WEHI-3B D+ cells, as measured by the band-depletion immunoblotting assay, while it did not affect the extractable topoisomerase II activity, measured by the unknotting of P4 phage DNA and by a DNA cleavage assay. Novobiocin progressively increased the steady-state concentration of intracellular VP-16. Removal of novobiocin resulted in a rapid return of VP-16 to levels comparable to those seen with VP-16 alone. The increased accumulation of VP-16 was accounted for by an increase in the exchangeable fraction only. The novobiocin-mediated increase in the steady-state concentration of VP-16 occurred whether novobiocin was added simultaneously with VP-16 or was added after a steady-state level of VP-16 had been achieved. Novobiocin did not affect the initial rate of uptake of VP-16; however, it inhibited the efflux of the epipodophyllotoxin. In fact, when cells were loaded with the same level of VP-16 in the presence or absence of novobiocin, the efflux curves in the presence or absence of novobiocin were significantly different. We conclude that the inhibition of VP-16 efflux by novobiocin is responsible for the increase in VP-16 accumulation, leading to increased formation of VP-16-stabilized topoisomerase-II-DNA covalent complexes and increased cytotoxicity.
Int J Cancer 1992 Dec 02
PMID:Novobiocin-induced accumulation of etoposide (VP-16) in WEHI-3B D+ leukemia cells. 133 54

The subunits of topoisomerase IV (topo IV), the ParC and ParE proteins in Escherichia coli, were purified to near homogeneity from the respective overproducers. They revealed type II topoisomerase activity only when they were combined with each other. In the presence of Mg2+ and ATP, topo IV was capable of relaxing a negatively or positively supercoiled plasmid DNA or converting the knotted P4 phage DNA, whether nicked or ligated, to a simple ring. However, supercoiling activity was not detected. The topoisomerase activity was not detectable when the purified ParC and ParE proteins were combined with the purified GyrB and GyrA proteins, respectively. This is consistent with the result that neither a parC nor a parE mutation was compensated by transformation with a plasmid carrying either the gyrA or the gyrB gene. Simultaneous introduction of both the gyrA and gyrB plasmids corrected the phenotypic defect of parC and parE mutants. The results suggest that DNA gyrase can substitute for topo IV at least in some part of the function for chromosome partitioning. Antisera were prepared against the purified ParC, ParE, GyrA, and GyrB proteins and used to investigate cellular localization of these gene products. ParC protein was found to be specifically associated with inner membranes only in the presence of DNA. This result suggests that one of the functions of topo IV might be to anchor chromosomes on membranes as previously proposed for eukaryotic topoisomerase II.
J Biol Chem 1992 Dec 25
PMID:Purification and characterization of DNA topoisomerase IV in Escherichia coli. 133 83


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