Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The action of luteinizing hormone on topoisomerase I activity from rat Leydig cells was studied. Stimulation of the enzyme was observed after long-term (24 and 48 h) gonadotrophin treatment in in vivo experiments. No change could be detected for shorter times than 12 h using two different experimental approaches. Topoisomerase I was stimulated by cAMP in a whole cell extract in a phosphorylation-dependent manner. These results suggest that topoisomerase I could be a target for nuclear events induced by peptide hormone action.
Mol Cell Endocrinol 1987 Oct
PMID:DNA topoisomerase I from Leydig cells is modulated by luteinizing hormone and cyclic adenosine monophosphate. 282 14

In Drosophila melanogaster the five histone genes are within a 5-kilobase region which is repeated 100 times at a single chromosomal site. These 5-kilobase repeats are of two distinct classes, short and long, that differ by approximately 200 base pairs of DNA in the spacer region between the H1 and H3 genes. Since the mRNA-homologous regions of the repeats are highly conserved, one cannot examine differential expression of the repeats by classical hybridization methods. In this study, we assessed their transcriptional activity by measuring in vivo the relative amounts of RNA polymerase II that were cross-linked by UV irradiation to the two different histone repeats. The RNA polymerase II density on the long repeat in Schneider line 2 cells was strikingly lower (10-fold) than the density on the short repeat. The magnitude of this difference cannot be accounted for by reduced transcription of only one or two genes of the repeat. The density of topoisomerase I, an indicator of transcriptional activity, was also much higher on the short repeat than on the long repeat of line 2 cells. In contrast, the RNA polymerase II density was slightly higher on the long repeat than on the short repeat in a second cell line, KcH. The major difference between active (KcH) and inactive (S2) long repeats resides in the H1-H3 nontranscribed spacer. This portion of the spacer may contain a component necessary for expression that can act over a moderate distance and affect multiple genes of the repeat.
Mol Cell Biol 1987 Sep
PMID:Protein-DNA cross-linking reveals dramatic variation in RNA polymerase II density on different histone repeats of Drosophila melanogaster. 282 28

We characterized a DNA repair system in frog oocytes by comicroinjection of UV-irradiated pBR322 DNA and radiolabeled nucleotides. Repair synthesis was monitored by incorporation of label into recovered pBR322 DNA and by a novel method in which the removal of UV photoproducts was determined from the shift of DNA topoisomers that occurs during gel electrophoresis upon repair of these lesions. We investigated the effects of several drugs in the oocyte system and found that although novobiocin, an inhibitor of topoisomerase II, was an effective inhibitor of repair, VM-26, another inhibitor of topoisomerase II, was not. In addition, the topoisomerase I inhibitor camptothecin had no effect on repair in this system. Finally, circular DNA (either supercoiled or nicked circular) was repaired at least 50 times more rapidly than linear DNA.
Mol Cell Biol 1987 Dec
PMID:Repair of UV-induced lesions in Xenopus laevis oocytes. 283 Apr 88

DNA supercoiling on the nucleosome was investigated by relaxing with topoisomerase I mono- and dinucleosomes reconstituted on small DNA rings. Besides 359 base-pair (bp) rings whose linking differences were integers, two additional series of rings with fractional differences, 341 and 354 bp in size, were used. Mononucleosomes reconstituted on 359 bp rings were found to relax into a single mononucleosome form. In contrast, 341 and 354 bp mononucleosomes relaxed into a mixture of two forms, corresponding to two adjacent topoisomers. The observation that the ratio between these two forms was, within each ring series, virtually independent of the initial linking number of the topoisomer used for the reconstitution suggested that each partition reflected an equilibrium. Comparison with the equilibria observed for the same rings in the absence of histones showed that the formation of a single nucleosome is associated with a linking number change of -1.1(+/-0.1) turn. Dinucleosomes, in contrast, were not relaxed to completion and do not reach equilibria. The corresponding linking number change per nucleosome was, however, estimated to be similar to the above figure, in agreement with previous data from the literature obtained with circular chromatins containing larger numbers of nucleosomes. DNA structure in mononucleosomes was subsequently investigated by means of high-resolution electron microscopy and gel electrophoresis. It was found that the above linking number reduction could be ascribed to a particle with a large open extranucleosomal DNA loop and with no more than 1.5 turns of a superhelix around the histone core. A theoretical model of a nucleosome on a small ring was constructed in which one part of the DNA was wrapped around a cylinder and the other part was free to vary both in torsion and flexion. The linking number reduction predicted was found to be most consistent with experimental data when the twist of the DNA in the superhelix was between 10.5 and 10.65 pb per turn, suggesting that wrapping on the nucleosome does not alter the twist of the DNA significantly. A lower estimate of the linking number reduction associated with a two-turn nucleosome was also derived, based on an analysis of recent data obtained upon treatment of reconstituted minichromosomes with gyrase. The value, 1.6 turns, set a lower limit of 10.44 bp per turn for the twist of nucleosomal DNA, in agreement with the above estimate.(ABSTRACT TRUNCATED AT 400 WORDS)
J Mol Biol 1988 Mar 20
PMID:Chromatin reconstitution on small DNA rings. II. DNA supercoiling on the nucleosome. 283 95

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 cAMP-containing phosphoform of the regulatory subunit (RII) of type II cAMP-dependent protein kinase from rat liver has been reported to have intrinsic DNA topoisomerase I activity. We found that highly purified RII preparations from eight different sources, including rat liver, contained no detectable topoisomerase I activity. Topoisomerase I exhibited an overlapping peak of activity with RII when rat liver extracts were fractionated by diethylaminoethyl-cellulose chromatography. Topoisomerase I activity was separated from RII by subsequent cAMP affinity chromatography. The results indicate that the regulatory subunit of cAMP-dependent protein kinase does not contain intrinsic topoisomerase I activity.
Mol Endocrinol 1988 Apr
PMID:Separation of topoisomerase I activity from the regulatory subunit of type II cyclic adenosine monophosphate-dependent protein kinase. 283 63

We have studied the effect of the antitumor drug, camptothecin, on the interaction of human topoisomerase I with DNA at the sequence level. At a low molar ratio of enzyme to DNA, cleavage is prominent and unique, located at a previously described hexadecameric recognition sequence, while a number of strong additional cleavage sites appear in the presence of the drug. Camptothecin stimulates cleavage at the recognition sequence less than twofold, whereas cleavage at the additional sites is stimulated up to 200-fold. Camptothecin greatly enhances the stability of the cleavable complexes formed at the additional sites, whereas the complex formed at the hexadecameric sequence is only marginally affected. Cleavage was eliminated at certain sites in the presence of camptothecin. Taken together these observations demonstrate that at least three types of potential eukaryotic topoisomerase I cleavage sites can be distinguished by the use of camptothecin. Comparison of the sequences at the additional cleavage sites in the presence of camptothecin reveals that the most frequently cleaved dinucleotide is TG with no consensus for the flanking nucleotides.
J Mol Biol 1988 Jul 20
PMID:Sequence-dependent effect of camptothecin on human topoisomerase I DNA cleavage. 284 97

The budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe are both sensitive to camptothecin, an inhibitor of DNA topoisomerase I. An S. cerevisiae DNA repair mutant, rad52, is hypersensitive to the drug. In both species, topoisomerase I mutants totally lacking the enzyme are completely resistant to the drug. A strain with a mutation leading to a temperature-sensitive topoisomerase I exhibits temperature dependence in its in vivo response to camptothecin. A strain carrying a plasmid that overproduces topoisomerase I is hypersensitive to the drug. The rad52 mutant is killed by overproduction of the enzyme, even in the absence of the drug. The response of several of these strains to camptothecin analogs, to DNA topoisomerase II inhibitors, and to other drugs is reported. The cytotoxic effects of camptothecin are discussed in terms of the drug extending the lifetime of a topoisomerase I-DNA covalent intermediate, which is recognized as DNA damage by a DNA repair system.
Mol Pharmacol 1988 Dec
PMID:Evidence that DNA topoisomerase I is necessary for the cytotoxic effects of camptothecin. 284 43

In the chromatin of Dictyostelium ribosomal RNA (rRNA) genes, the coding and upstream flanking regions are sensitive to endonucleases. This sensitivity stops about 2.3 x 10(3) bases upstream from the transcription start, at a point we call the structural boundary. Upstream from the boundary an 850 base-pair region is strongly protected against micrococcal nuclease cleavage, particularly in rapidly transcribing vegetative cells, and upstream from this the pattern of nuclease protection suggests that positioned nucleosomes are present. On the gene side of the structural boundary nucleosomes are known to be absent in vegetative cells but present in differentiating slug cells where the rRNA synthesis rate is lower. We show that in slugs these nucleosomes are randomly distributed, in contrast to those upstream from the boundary. Close to the gene side of the boundary is a duplication of the putative promoter located 29 base-pairs distant from four clustered topoisomerase I recognition sequences, which are cleaved by endogenous topoisomerase I-like activity. An additional topoisomerase I recognition sequence found upstream from the structural boundary is not cleaved in chromatin. The possible significance of these sequences and structures in transcription is discussed.
J Mol Biol 1988 Dec 05
PMID:The upstream limit of nuclease-sensitive chromatin in Dictyostelium rRNA genes neighbors a topoisomerase I-like cluster. 285 57

Permeabilized nuclei from mammalian cells encapsulated within agarose microbeads in an isotonic buffer are active in transcription and replication (Jackson, D. A., and P. R. Cook. 1985. EMBO (Eur. Mol. Biol. Organ.) J. 4:913-918). Their DNA is intact and the nuclei are accessible to macromolecules. Myeloma nuclei prepared in this way were used to probe the extent of DNA negative supercoiling and the effects of altering torsional strain by binding radioactively labeled monoclonal antibodies to Z-DNA. Control experiments used monoclonal antibodies against a nonhistone chromosomal protein, HMG-17. On increasing the amount of anti-HMG-17 added, a binding plateau was reached encompassing a 200-fold range of antibody concentration. On binding anti-Z-DNA antibody, a similar broad plateau of constant binding was found encompassing a 100-fold range of antibody concentration. The latter result was taken as a measure of preexisting Z-DNA in the nuclei. Additional anti-Z-DNA antibody binding can be "induced" in the presence of much higher concentration of antibody, apparently by perturbing the B-DNA/Z-DNA equilibrium. On inhibiting topoisomerase I with camptothecin, an elevated antibody binding plateau was found, suggesting that elastic torsional strain in the DNA is responsible for stabilizing the preexisting Z-DNA. This interpretation is supported by the fact that addition of small, nicking amounts of DNase I leads to a complete loss of antibody binding in the Z-DNA plateau region but not in the region of "induced" Z-DNA.
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PMID:The level of Z-DNA in metabolically active, permeabilized mammalian cell nuclei is regulated by torsional strain. 292 Dec 82


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