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)

We have found that type II topoisomerase inhibitors have two effects on replicating simian virus 40 genomes in vivo: production of catenated dimers and slowed replication of the last 5% of the genome. This suggests that type II topoisomerase simultaneously decatenates and facilitates replication fork movement at this stage of DNA replication. On the basis of this observation, a detailed model is proposed for the roles of topoisomerases I and II in simian virus 40 DNA replication.
Mol Cell Biol 1988 Feb
PMID:Swiveling and decatenation of replicating simian virus 40 genomes in vivo. 283 24

Sites of an endogenous activity that has the properties of a DNA topoisomerase I have been identified on the palindromic ribosomal RNA genes of the slime mould Dictyostelium discoideum. This was done in vitro, by treating isolated nuclei with sodium dodecyl sulphate, which denatures topoisomerase during its cycle of nicking, strand passing and resealing, and hence reveals the DNA cleavages. It was also done in vivo using the drug camptothecin, which is believed to stabilize the cleavable complex of topoisomerase I plus DNA, hence increasing the chances of cleavage when sodium dodecyl sulphate is subsequently added. The cleavages in vitro and in vivo were mapped by indirect end-labelling. Both treatments cause what appear to be strong double-stranded cleavages at 200 and 2200 base-pairs and at 17 X 10(3) base-pairs upstream from the rRNA transcription start. The cleavage at 200 base-pairs was analysed in greater detail using RNA hybridization probes specific for single DNA strands. The cleavage is in fact composed of three closely spaced nicks on each DNA strand. The DNA sequence at each of the nicks is strongly homologous across 15 base-pairs. Sodium dodecyl sulphate-induced cleavage by eukaryotic topoisomerase I is known to yield enzyme covalently attached to the 3' cut end of the DNA. We show that protein-linked DNA restriction fragments with their 3' ends at the cleavage sites are selectively retarded on denaturing gels, which provides strong evidence that the unusual cluster of cleavages is caused by a topoisomerase I. Additionally, the camptothecin results revealed cleavages not only at the specific upstream sites, but also across the transcribed region. Interestingly, the zone of camptothecin-assisted cleavage does not extend as far at the 3' end of the gene as the zone of endogenous nuclease sensitivity.
J Mol Biol 1988 Mar 05
PMID:Topoisomerase I cleavage sites identified and mapped in the chromatin of Dictyostelium ribosomal RNA genes. 283 75

The PRL gene is expressed at a high basal level in rat pituitary tumor GH3 cells, and this basal level enhancement of PRL gene expression is maintained through a Ca2+-calmodulin-dependent mechanism. We have now examined whether the enzyme, DNA topoisomerase II, which has been shown to be phosphorylated by a Ca2+-calmodulin-dependent protein kinase, plays a role in the Ca2+-calmodulin-dependent basal level enhancement of PRL gene expression. The topoisomerase II inhibitor, novobiocin, at concentrations in the range of 35-140 microM, effectively blocked the ability of Ca2+ to increase PRL mRNA levels. Examination of the effects of novobiocin on the levels of protein synthesis, glucose-regulated protein (GRP) 78 mRNA, histone 3 mRNA, and 18S ribosomal RNA indicated that the drug selectivity inhibited PRL gene expression. Two other topoisomerase II inhibitors, m-AMSA and VM26, also diminished the Ca2+-induced levels of PRL mRNA at concentrations (100-400 nM) that did not lower total mRNA levels. We then examined whether topoisomerase II interacted nonrandomly with DNA from the 5' transcribed and 5'-flanking region of the rat PRL gene by in vitro mapping of topoisomerase II DNA cleavage sites. In initial assays with a 10.5 kilobase (kb) PRL genomic DNA fragment containing 3.5 kb of 5'-transcribed DNA and 7 kb of 5'-flanking DNA, we detected 4 major cleavage sites in the following regions: site 1, +1500 to +1600; site 2, +1 to -100; site 3, -1200 to -1300; and site 4, -2900 to -3000.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1988 Jan
PMID:Evidence for a role of topoisomerase II in the Ca2+-dependent basal level expression of the rat prolactin gene. 284 May 67

The type II topoisomerase of bacteriophage T4 is a central determinant of the frequency and specificity of acridine-induced frameshift mutations. Acridine-induced frameshift mutagenesis is specifically reduced in a mutant defective in topoisomerase activity. The ability of an acridine to promote topoisomerase-dependent cleavage at specific DNA sites in vitro is correlated to its ability to produce frameshift mutations at those sites in vivo. The specific phosphodiester bonds cleaved in vitro are precisely those at which frameshifts are most strongly promoted by acridines in vivo. The cospecificity of in vitro cleavage and in vivo mutation implicate acridine-induced, topoisomerase-mediated DNA cleavages as intermediates of acridine-induced mutagenesis in T4.
J Mol Biol 1988 Apr 20
PMID:Hotspot sites for acridine-induced frameshift mutations in bacteriophage T4 correspond to sites of action of the T4 type II topoisomerase. 284 8

Previous evidence suggests that epipodophyllotoxins, such as etoposide and teniposide, and the N-acyl anthracycline AD41 inhibit topoisomerase II resealing even though they apparently do not bind to DNA. Using experimental conditions designed to detect limited numbers of DNA binding sites, we now report that both epipodophyllotoxins and the N-acyl anthracyclines AD41 and AD32 bind to DNA. Binding was greater to kinetoplast DNA than to pUC18 plasmid DNA. There was also greater etoposide binding to single-stranded DNA than to double-stranded linear or supercoiled DNA. Based on binding competition experiments, etoposide and teniposide appear to have equal affinity for DNA, in spite of the fact that the latter is more potent as a topoisomerase inhibitor. This suggests that the difference in the drugs relates to protein interaction. There are 3- to 7-fold more binding sites for AD41 than for AD32, depending on the DNA substrate employed, and both drugs, unlike adriamycin, exhibit saturation of binding sites over a concentration range of 0-50 microM when kinetoplast DNA is the substrate. Evidence for DNA intercalation by AD41 is provided by the observation that the drug introduces positive supercoils into covalently closed plasmid DNA. Based on these data, a hypothesis is proposed that would provide a general mechanism whereby intercalating agents and epipodophyllotoxins alter topoisomerase function and presumably exert their antitumor effects.
Mol Pharmacol 1988 Oct
PMID:DNA binding by epipodophyllotoxins and N-acyl anthracyclines: implications for mechanism of topoisomerase II inhibition. 284 48

A novobiocin-resistant BHK cell line, designated as NovrA2, was found to exhibit cross-resistance to other topoisomerase II inhibitors such as 4'-dimethylepipodophyllotoxin-4-(4,6-O-ethylidine-beta-D-glu copyranoside) (VP-16), adriamycin, and 4'-(9-acridinyl-amino)methanesulfon-m-anisidide (m-AMSA), and also to different types of drugs such as vinblastine and arabinocytidine. Nalidixic acid-resistant cells (A2Nalr) of the NovrA2 cell line were phenotypically reverted to novobiocin sensitivity like wild-type cells and were also partially reverted to sensitivity to VP-16 and adriamycin, but not to vinblastine and arabinocytidine. When VP-16 was added to cell culture, the drug-induced DNA strand breaks were much fewer in NovrA2 cells than in BHK cells. This reduced level of strand breaks in NovrA2 cells was not due to reduced drug uptake, because the two cell lines accumulated similar levels of radiolabeled VP-16. VP-16 also induced fewer DNA breaks in isolated nuclei of NovrA2 cells than in those of BHK cells. There was no significant difference in the VP-16-induced DNA cleavage activities of partially purified topoisomerase II from BHK and Novr cells. These results show that the resistance of NovrA2 cells to various drugs is not acquired by a defense mechanism related to membrane permeability and suggest that the resistance of the NovrA2 cells to topoisomerase II inhibitors might be due in part to alteration in a topoisomerase II associated factor(s).
Somat Cell Mol Genet 1988 Sep
PMID:Cross-resistance of novobiocin-resistant BHK cell line to topoisomerase II inhibitors. 284 88

The structure of replicating simian virus 40 minichromosomes, extracted from camptothecin-treated infected cells, was investigated by biochemical and electron microscopic methods. We found that camptothecin frequently induced breaks at replication forks close to the replicative growth points. Replication branches were disrupted at about equal frequencies at the leading and the lagging strand sides of the fork. Since camptothecin is known to be a specific inhibitor of type I DNA topoisomerase, we suggest that this enzyme is acting very near the replication forks. This conclusion was supported by experiments with aphidicolin, a drug that blocks replicative fork movement, but did not prevent the camptothecin-induced breakage of replication forks. The drug teniposide, an inhibitor of type II DNA topoisomerase, had only minor effects on the structure of these replicative intermediates.
Mol Cell Biol 1988 Aug
PMID:Camptothecin, a specific inhibitor of type I DNA topoisomerase, induces DNA breakage at replication forks. 285 Apr 77

Endogenous topoisomerase II cleavage sites were mapped in the chicken beta A-globin gene of 12- to 14-day embryonic erythrocytes. A major topoisomerase II catalytic site was mapped to the 5' end of the globin gene which contained a nucleosome-free and DNase I-hypersensitive site and additional but minor sites were mapped to the second intron and 3' of the gene to a tissue-specific enhancer. Cleavage sites, mapped in situ by indirect end labeling, were aligned to single-base-pair resolution by comparison to a consensus sequence derived for vertebrate topoisomerase II catalytic sites. In contrast to embryonic erythrocytes, endogenous topoisomerase II cleavages were not detected in erythrocytes from peripheral blood of adult chickens; therefore, as the transcriptional activity of the beta A-globin gene declines during terminal differentiation of erythrocytes, the activity of topoisomerase II in situ declines as well, despite the fact that DNase I hypersensitivity persists. The results showed that DNase I-hypersensitive chromatin can be maintained in the absence of topoisomerase II activity and suggested that topoisomerase II acts at hypersensitive sites because of an inherent attraction to some preexisting combination of DNA sequence or chromatin structure associated with DNase I-hypersensitive regions.
Mol Cell Biol 1988 Sep
PMID:DNase I hypersensitivity is independent of endogenous topoisomerase II activity during chicken erythrocyte differentiation. 285 23

Recently, the antitumor agent 4'-(9-acridinylamino)-methanesulfon-m-anisidide (m-AMSA) was shown to revert a frameshift mutant of T4 (rFC11), and its mutagenicity was shown to be mediated by T4 DNA topoisomerase II [Ripley et al.: J Mol Biol 200: 665-680, 1988]. Here we report dose-response data on the mutagenicity and toxicity of m-AMSA in T4 rFC11. We find that m-AMSA is among the most potent frameshift mutagens observed in T4, inducing a 10-fold increase in mutant frequency in the absence of toxicity and a 500-fold increase in mutant frequency at 31% survival. In addition to m-AMSA, the topoisomerase-active agents ellipticine, oxolinic acid, and nalidixic acid also reverted rFC11; however, they required concentrations 10-100 times greater than those required by m-AMSA in order to be mutagenic, and they did not produce mutant frequencies as high as those produced by m-AMSA. Unlike m-AMSA, all three agents were mutagenic only at toxic doses. The other agents evaluated--actinomycin D, adriamycin, 9-aminoellipticine, 9-methoxyellipticine, teniposide (VM-26), and novobiocin--were toxic but not mutagenic to T4 rFC11. Thus, m-AMSA appears to be distinctly different from the other topoisomerase-active agents in exhibiting such potent mutagenic activity in T4 rFC11. Because E. coli DNA gyrase may substitute for T4 topoisomerase II, we examined the ability of two inhibitors of E. coli DNA gyrase, novobiocin and nalidixic acid, to inhibit m-AMSA's mutagenicity. Both agents substantially reduced the mutagenicity of m-AMSA in T4 rFC11, further suggesting that topoisomerase mediates the mutagenicity of m-AMSA.
 ...
PMID:Mutagenicity of topoisomerase-active agents in bacteriophage T4. 290 38

We have previously described an isolated kinetoplast system from Crithidia fasciculata capable of ATP-dependent replication of kinetoplast DNA minicircles (L. Birkenmeyer and D.S. Ray, J. Biol. Chem. 261: 2362-2368, 1986). We present here the identification of two new minicircle species observed in short pulse-labeling experiments in this system. The earliest labeled minicircle species (component A) contains both nascent H and L strands and is heterogeneous in sedimentation and electrophoretic migration. Component A has characteristics consistent with a Cairns-type structure in which the L strand is the leading strand and the H strand is the lagging strand. The other new species (component B) has a nascent 2.5-kilobase linear L strand with a single discontinuity that mapped to either of two alternative origins located 180 degrees apart on the minicircle map. Component B could be repaired to a covalently closed form by Escherichia coli polymerase I and T4 ligase but not by T4 polymerase and T4 ligase. Even though component B has a single gap in one strand, it had an electrophoretic mobility on an agarose gel (minus ethidium bromide) similar to that of a supercoiled circle with three supertwists. Treatment of component B with topoisomerase II converted it to a form that comigrated with a nicked open circular form (replicative form II). These results indicate that component B is a knotted topoisomer of a kinetoplast DNA minicircle with a single gap in the L strand.
Mol Cell Biol 1989 Jan
PMID:Replication of DNA minicircles in kinetoplasts isolated from Crithidia fasciculata: structure of nascent minicircles. 292 90


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