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)

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.
Cold Spring Harb Symp Quant Biol 1978
PMID:Biochemical and ultrastructural analysis of SV40 chromatin. 20 38

We have undertaken a genetic analysis of heat-sensitive and cold-sensitive mutations in TOP2, the gene encoding yeast DNA topoisomerase II. Deletion mapping was used to localize 14 heat-sensitive and four cold-sensitive top2 mutations created by a method biased toward mutations in the 3' two-thirds of the gene. The mutations all appear to be located in the region of DNA topoisomerase II that shows homology to the "A" subunit of bacterial DNA gyrase. The heat-sensitive mutations and one cold-sensitive mutation lie in the center of the gene near the sequence that encodes the active site tyrosine. The three other cold-sensitive mutations map farther toward the 3' end of the gene. The cold-sensitive mutations exhibit intragenic complementation, and the complementation groups correspond to the physical map. We sequenced nine top2 mutations and found that the mutations are usually single missense mutations, frequently involve proline, and affect conserved regions of the protein. Suppressor analysis yielded two intragenic suppressors and seven independent isolates of an allele-specific extragenic suppressor we named tos1; tos1 is not allelic to any genes predicted to encode type I topoisomerase-related proteins. The two intragenic suppressors were tested for allele-specificity; the results revealed a complex pattern of suppression between heat-sensitive and cold-sensitive top2 alleles. These top2 mutations may have compensatory effects on the general stability of the protein.
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PMID:Genetic analysis of the gyrase A-like domain of DNA topoisomerase II of Saccharomyces cerevisiae. 165 64

To understand better the similarities and differences between meiosis and mitosis, we examined the meiotic role of DNA topoisomerase II, an enzyme that is required mitotically to disentangle sister chromatids at the time of chromosome segregation. In meiosis, we found that topoisomerase II is required only at the time of nuclear division. When cold-sensitive top2 mutants are induced to sporulate at the restrictive temperature, they undergo premeiotic DNA synthesis and commitment to meiotic levels of recombination but fail to complete the first meiotic nuclear division. The introduction of a mutation blocking recombination relieves the requirement for topoisomerase II in meiosis I. These results suggest that topoisomerase II is required at the time of chromosome segregation in meiosis I for the resolution of recombined chromosomes.
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PMID:Segregation of recombined chromosomes in meiosis I requires DNA topoisomerase II. 215 24

We isolated two novobiocin-resistant mutants which were stable and approximately three and four times more resistant than the parent cells to novobiocin. Both mutants (Novr A2, Novr A41) were more sensitive than the wild-type cells to nalidixic acid, and cold sensitive for cell growth. When we isolated derivatives of Novr A2 and Novr A41 cells which are resistant to nalidixic acid, those are found to be phenotypically reverted to novobiocin sensitivity like wild-type cells, thereby suggesting the relationship between the targets for novobiocin and for nalidixic acid. But the cold sensitivity did not always revert to wild type, with accompanying resistance to nalidixic acid. The DNA and RNA syntheses of Novr mutants were more resistant to novobiocin but more sensitive to nalidixic acid, than those of wild-type cells. However, in vitro assays of wild-type and Novr cell extracts were unable to demonstrate any differences in the sensitivity of topoisomerase II activity to inhibition by novobiocin. While the targets of novobiocin and nalidixic acid show a mutual interaction in vivo and play a role in DNA replication and transcription, our results suggest that these targets are probably not topoisomerase II.
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PMID:Isolation and characterization of novobiocin-resistant BHK cells. 243 72

We cloned MAK11, MAK18, and MKT1 utilizing their genetic map positions. The MAK11 gene is close to CDC16 on chromosome XI. Both genes were cloned on a single 7-kb fragment, and both have now been sequenced. The MAK18 gene is located close to PET3 on chromosome VIII. A large plasmid carrying PET3 was obtained from R. Elder and R.E. Esposito and was found to also have the MAK18 gene. The MAK16 gene has been subcloned and sequenced starting with a clone provided by J. Crowley and D. Kaback. The MKT1 gene was mapped near the gene for topoisomerase II. The topoisomerase II clone was used as the starting point for chromosome-walking to isolate MKT1. A deletion-insertion mutation (disruption) of MKT1 results in an inability to maintain M2, but does not affect M1 or L-A maintenance. Clones of SKI3 and SKI8 were selected using the cold sensitivity for cell growth of ski- M1 strains. The SKI8 gene was disrupted and found to be nonessential for cell growth in the absence of M double-stranded RNA (dsRNA). The SKI3 and SKI8 genes were mapped using these clones. We have also obtained other clones suppressing the pathology caused by the high M titer in ski- strains. These clones are not the SKI genes themselves but somehow avoid the growth defect without repressing M copy number.
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PMID:Molecular characterization of chromosomal genes affecting double-stranded RNA replication in Saccharomyces cerevisiae. 355 12

We have asked, "What is the mechanism of strand exchange during site-specific recombination of phage lambda?" Crosses carried out in vivo have shown that the recombination joint can be extended rather than flush and that the four-strand breaks and rejoinings needed to from a recombinant can occur asynchronously. Crosses carried out in vitro have shown that all the nucleotides at the site of crossover are conserved during recombination, as are most or all of the superhelical turns present in the substrate molecules. We have presented new data showing that topoisomerase activity of Int protein relaxes DNA by making transient single-strand, rather than double-strand, breaks in the phosphodiester back-bone. These findings are incorporated into a model for strand exchange that has as its central intermediate a four-strand structure.
Cold Spring Harb Symp Quant Biol 1981
PMID:Strand exchange in lambda integrative recombination: genetics, biochemistry, and models. 627 87

The chemotherapeutic drug etoposide (VP-16) causes the equilibrium reaction between noncleavable and cleavable topoisomerase II-DNA complexes to shift in favor of the cleavabel complex [H. Zang, P. D'Arpa, and L.F. Liu, Cancer Cells (Cold Spring Harbor), 2:23-27, 1990]. Pulsed-field gel electrophoresis was used to study induction and removal of cleavable complexes in cells heated before, during, or after VP-16 treatment. Pulsed-field gel electrophoresis results were evaluated both as the fraction of activity (DNA) released from the plug and as the number of double-strand breaks (DSBs) calculated from molecular weight distributions; both end points led to the same conclusions. When cells were heated at 42 degrees C during treatment with VP-16 (12 micrograms/ml up to 60 min), a slight decrease in cleavable complexes (from 30 to 20 DSBs/100 megabase pairs) was detected immediately after treatment when compared with cells treated with the drug at 37 degree C. Furthermore, heating at 42 degrees C caused a slight decrease in drug cytotoxicity as measured by less than a 2-fold increase in clonogenic survival. When cells were heated for 10 min at 45.5 degrees C prior to or after treatment with the drug, there was a reduction (approximately 50%) immediately after treatment in the number of DSBs/100 megabase pairs compared with unheated cells. The rate of removal of cleavable complexes was decreased slightly by heat. After 120 min at 37 degrees C, the number of DSB/100 megabase pairs decreased to approximately 6 for both unheated cells and those heated prior to drug treatment and to approximately 8 for cells heated after drug treatment. In agreement with a low effect of heat on the number of cleavable complexes after drug treatment, there was no significant effect of this heating protocol on drug cytotoxicity. However, heating at 45.5 degrees C prior to drug treatment at 37 degrees C protected cells from drug cytotoxicity (e.g., increased survival after 12 micrograms/ml for 60 min by approximately 100-fold) despite the similarity in the induction and rate of removal of cleavable complexes when compared with nonheated cells. Thus, when cells are heated prior to administration of VP-16, drug cytotoxicity does not correlate with the number of cleavable complexes measured either immediately after treatment or 180 min later when approximately 75% of the initial number have been removed. Finally, since hyperthermia can actually decrease drug cytotoxicity, the use of hyperthermia as an adjuvant to chemotherapy involving topoisomerase II poisons, such as VP-16, should be approached with caution.
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PMID:Hyperthermia can reduce cytotoxicity from etoposide without a corresponding reduction in the number of topoisomerase II-DNA cleavable complexes. 803 46

The recently developed procedure of chromosomal DNA loop excision by topoisomerase II-mediated DNA cleavage at matrix attachment sites (S. V. Razin, R. Hancock, O. Iarovaia, O. Westergaard, I. Gromova, and G. P. Georgiev, Cold Spring Harbor Symp. Quant. Biol. 58:25-35, 1993; I. I. Gromova, B. Thompsen, and S. V. Razin, Proc. Natl. Acad. Sci. USA 92:102-106, 1995) has been employed for mapping the DNA loop anchorage sites in a 500-kb region of the Drosophila melanogaster X chromosome. Eleven anchorage sites delimiting 10 DNA loops ranging in size from 20 to 90 kb were found within this region. Ten of these 11 anchorage sites colocalize with previously mapped scaffold attachment regions. However, a number of other scaffold attachment regions are found to be located in loop DNA.
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PMID:Mapping of genomic DNA loop organization in a 500-kilobase region of the Drosophila X chromosome by the topoisomerase II-mediated DNA loop excision protocol. 852 9

A mouse mammary carcinoma FM3A cell line resistant to the DNA topoisomerase (topo) II-targeting agent, etoposide (VP-16), FM3A/VP-2B, had a markedly reduced growth rate at a low temperature (33 degrees C). The cells had the following properties: (a) FM3A/VP-2B, which had 24-fold higher resistance to VP-16 than its parental line, FM3A, was cross-resistant to doxorubicin, but not to a camptothecin derivative, CPT-11. (b) Cold-resistant revertants from FM3A/VP-2B, R-6 and R-11, remained 8- to 9-fold more resistant to VP-16 and 2- to 3-fold more resistant to doxorubicin. (c) FM3A/VP-2B had one-fourth the level of topo II activity and one-third of the topo II alpha content and mRNA of FM3A. R-6 and R-11, however, had levels similar to FM3A. (d) FM3A/VP-2B and FM3A had a 3-base deletion at position 4170 on one allele on the topo II alpha cDNA, but expression of the wild-type and the deletion allele was not appreciably changed in both cell lines. Decreased topo II alpha expression might have led to the acquisition of drug resistance to etoposide in FM3A/VP-2B, and appeared to be linked with the cold-sensitive growth. We also present a corrected mouse topo II alpha cDNA sequence.
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PMID:Decreased DNA topoisomerase II alpha expression and cold-sensitive growth in a mouse mammary cancer cell line resistant to etoposide and doxorubicin. 888 12

Plasmid topology varies transiently in hyperthermophilic archaea during thermal stress. As in mesophilic bacteria, DNA linking number (Lk) increases during heat shock and decreases during cold shock. Despite this correspondence, plasmid DNA topology and proteins presumably involved in DNA topological control in each case are different. Plasmid DNA in hyperthermophilic archaea is found in a topological form from relaxed to positively supercoiled in contrast to the negatively supercoiled state typical of bacteria, eukaryotes and mesophilic archaea. We have analysed the regulation of DNA topological changes during thermal stress in Sulfolobus islandicus (kingdom Crenarchaeota), which harbours two plasmids, pRN1 and pRN2. In parallel with plasmid topological variations, we analysed levels of reverse gyrase, topoisomerase VI (Topo VI) and the small DNA-binding protein Sis7, as well as topoisomerase activities in crude extracts during heat shock from 80 degrees C to 85-87 degrees C, and cold shock from 80 degrees C to 65 degrees C. Quantitative changes in reverse gyrase, Topo VI and Sis7 were not significant. In support of this, inhibition of protein synthesis in S. islandicus during shocks did not alter plasmid topological dynamics, suggesting that an increase in topoisomerase levels is not needed for control of DNA topology during thermal stress. A reverse gyrase activity was detected in crude extracts, which was strongly dependent on the assay temperature. It was inhibited at 65 degrees C, but was greatly enhanced at 85 degrees C. However, the intrinsic reverse gyrase activity did not vary with heat or cold shock. These results suggest that the control of DNA topology during stress in Sulfolobus relies primarily on the physical effect of temperature on topoisomerase activities and on the geometry of DNA itself. Additionally, we have detected an enhanced thermoresistance of reverse gyrase activities in cultures subject to prolonged heat shock (but not cold shock). This acquired thermotolerance at the enzymatic level is abolished when cultures are treated with puromycin, suggesting a requirement for protein synthesis.
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PMID:Control of DNA topology during thermal stress in hyperthermophilic archaea: DNA topoisomerase levels, activities and induced thermotolerance during heat and cold shock in Sulfolobus. 1044 86


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