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

---

Query: EC:5.99.1.3 (topoisomerase)
9,911 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Changes in nuclear structure and chromatin composition regulate gene activity in many cell types and could play a similar role during early mammalian embryogenesis. Oocytes of the mouse contain the three major lamin species present in somatic cells, although lamin A synthesized by oocytes has a higher molecular mass than the somatic species. Oocyte chromatin contains core histones similar to those of somatic cells, as well as elements that are immunologically related to protamines. In contrast, somatic-type histone H1 is not present. DNA topoisomerase II has not yet been identified in mammalian oocytes, but is abundant in frog oocytes. In contrast to oocytes, sperm do not contain a typical nuclear lamina. DNA topoisomerase II is detectable until late spermiogenesis. Although the DNA of sperm is associated mainly with protamines, some histone may be retained. There is also evidence that the arrangement of the DNA in the nucleus is nonrandom. These results demonstrate differences in nuclear and chromatin composition between oocytes and sperm. After fertilization, the nuclei of cleavage-stage blastomeres undergo programmed modifications. Lamin B is synthesized, whereas lamin A is not. In addition, a set of nuclear proteins is transiently synthesized in mice at the two-cell stage. Changes in embryonic chromatin composition also occur. The relative abundance of transcripts from different core histone genes differs between mouse oocytes and blastocysts. Furthermore, somatic histone H1 becomes detectable beginning at the mid-four-cell stage. As well, during early cleavage stages, expression of plasmid-borne genes becomes dependent on enhancers. Thus, developmentally regulated changes in nuclear and chromatin composition occur during early mammalian embryogenesis, and these may be important for the initiation and regulation of embryonic gene activity.
...
PMID:Nuclear and chromatin composition of mammalian gametes and early embryos. 129 51

The recent discovery of DNA sequences responsible for the specific attachment of chromosomal DNA to the nuclear skeleton (MARs/SARs) was an important step towards our understanding of the functional and structural organization of eukaryotic chromatin [Mirkovitch et al.: Cell 44:273-282, 1984; Cockerill and Garrard: Cell 44:273-282, 1986]. A most important question, however, remains the nature of the matrix proteins involved in the specific binding of the MARs. It has been shown that topoisomerase II and histone H1 were capable of a specific interaction with SARs by the formation of precipitable complexes [Adachi et al.: EMBO J8:3997-4006, 1989; Izaurralde et al.: J Mol Biol 210:573-585, 1989]. Here, applying a different approach, we were able to "visualize" some of the skeletal proteins recognizing and specifically binding MAR-sequences. It is shown that the major matrix proteins are practically the same in both salt- and LIS-extracted matrices. However, the relative MAR-binding activity of the individual protein components may be different, depending on the method of matrix preparation. The immunological approach applied here allowed us to identify some of the individual MAR-binding matrix proteins. Histone H1 and nuclear actin are shown to be not only important components of the matrix, but to be involved in a highly efficient interaction with MAR-sequences as well. Evidence is presented that proteins recognized by the anti-HMG antibodies also participate in MAR-interactions.
...
PMID:Interaction of MAR-sequences with nuclear matrix proteins. 133 Nov 26

Monoclonal antibodies directed against four different polypeptide epitopes on the Mr approximately 94,000 steroid-binding subunit of the rat liver cytosolic glucocorticoid receptor (GcR) were used to probe Western blots of epididymal spermatozoa from rats and mice. Two sperm polypeptides with apparent molecular weights of 94,000 (indistinguishable in size from the liver GcR subunit) and 150,000 reacted with these antibodies. Other polypeptides that are present in a wide variety of somatic cells [lamin-A, -B, and -C; topoisomerase-I; poly(ADP-ribose) polymerase; the 62-kilodalton internal nuclear matrix protein; the nucleolar protein B23; and histone H1] could not be detected in these preparations of spermatozoa, thus appearing to rule out contamination by somatic cells. Rat and mouse pachytene spermatocytes and round spermatids contained much lower amounts of the Mr approximately 94,000 and 150,000 polypeptides. These results suggested that the steroid-binding subunit of the GcR might be accumulated late in spermatogenesis. Consistent with this view, a 6-kilobase mRNA (identical in size to a mRNA detected in mouse somatic cell lines) was detected when Northern blots of mouse round spermatid RNA were probed with a cDNA to the steroid-binding GcR subunit. Although the results described above suggest the presence of GcR in rodent sperm, high affinity binding of glucocorticoids to epididymal sperm could not be detected in a whole cell binding assay. Further analysis revealed that the Mr approximately 90,000 heat shock protein (hsp90), a component reportedly required for high affinity ligand binding to the GcR, was present in early germ cells, but absent from rodent epididymal sperm. These results suggest that the Mr approximately 94,000 steroid-binding subunit of the GcR and an immunologically related Mr approximately 150,000 polypeptide are specifically accumulated during the later stages of rodent spermatogenesis, but are not assembled into receptor complexes capable of binding steroid. In addition, these results support the view that hsp90 is required for high affinity binding of glucocorticoids to the Mr approximately 94,000 GcR subunit in intact cells.
...
PMID:Evidence that rodent epididymal sperm contain the Mr approximately 94,000 glucocorticoid receptor but lack the Mr approximately 90,000 heat shock protein. 157 14

Assembly of nucleosomes on relaxed, covalently closed DNA has been studied in a nuclear extract of Xenopus laevis oocytes. Nucleosomes containing the four histones H3, H4, H2A and H2B but lacking histone H1 are readily assembled on the DNA. The pattern of micrococcal nuclease digestion shows that the nucleosomes assembled in the absence of ATP and Mg (II) are closely packed, with a periodicity of 150 base pairs (bp). In contrast, in the presence of ATP and Mg (II) the spacing of the nucleosomes is 180 bp, similar to that observed for nucleosomes assembled on DNA microinjected into oocyte nuclei. The ATP and Mg (II) requirements for the assembly of correctly spaced nucleosomes are unrelated to the activity of the ATP and Mg (II) dependent DNA topoisomerase II in the extract; addition of specific inhibitors of eukaryotic DNA topoisomerase II has no effect on the spacing of the reconstituted nucleosomes. The ATP requirement in the assembly of correctly spaced nucleosomes can be substituted by adenosine 5'-O-3'-thiotriphosphate (gamma-S-ATP) but not by adenyl-5'-yl imidodiphosphate (AMP-P-(NH)-P).
...
PMID:Assembly of correctly spaced chromatin in a nuclear extract from Xenopus laevis oocytes. 217 Sep 36

We have examined the effects of topoisomerase inhibitors on the phosphorylation of histones in chromatin during the G2 and the M phases of the cell cycle. Throughout the G2 phase of BHK cells, addition of the topoisomerase II inhibitor VM-26 prevented histone H1 phosphorylation, accompanied by the inhibition of intracellular histone H1 kinase activity. However, VM-26 had no inhibitory effect on the activity of the kinase in vitro, suggesting an indirect influence on histone H1 kinase activity. Entry into mitosis was also prevented, as monitored by the absence of nuclear lamina depolymerization, chromosome condensation, and histone H3 phosphorylation. In contrast, the topoisomerase I inhibitor, camptothecin, inhibited histone H1 phosphorylation and entry into mitosis only when applied at early G2. In cells that were arrested in mitosis, VM-26 induced dephosphorylation of histones H1 and H3, DNA breaks, and partial chromosome decondensation. These changes in chromatin parameters probably reverse the process of chromosome condensation, unfolding condensed regions to permit the repair of strand breaks in the DNA that were induced by VM-26. The involvement of growth-associated histone H1 kinase in these processes raises the possibility that the cell detects breaks in the DNA through their effects on the state of DNA supercoiling in constrained domains or loops. It would appear that histone H1 kinase and topoisomerase II work coordinately in both chromosome condensation and decondensation, and that this process participates in the VM-26-induced G2 arrest of the cell.
...
PMID:The topoisomerase II inhibitor VM-26 induces marked changes in histone H1 kinase activity, histones H1 and H3 phosphorylation, and chromosome condensation in G2 phase and mitotic BHK cells. 217 57

Protein-DNA interactions within the promoter of a cell cycle-regulated human H4 histone gene were examined by binding of 5'-end-labeled DNA segments to Western blots of nuclear protein fractions. Specific protein interactions were observed with DNA segments located between -500 bp and -1,070 bp upstream of the ATG initiation codon and included a histone H1 binding segment flanked on both sides by binding sites for a 45 kD nuclear protein. This region of the gene contains a DNase I-sensitive site in the center (-720 to -820 bp), and sequence analysis revealed the presence of scaffold attachment sequences in the two flanking segments. Topoisomerase II consensus sequences and in vitro topoisomerase II cleavage sites were also detected in the two flanking segments. Our results suggest that the 45 kd nuclear protein may preferentially interact with these two segments of the H4 histone gene to mediate association with the nuclear matrix. The presence of negative regulatory elements in this putative matrix attachment region provides a basis for the speculation that such nuclear proteins are associated with alterations in gene-matrix interaction that are functionally related to gene expression.
...
PMID:Specific interactions of histone H1 and a 45 kilodalton nuclear protein with a putative matrix attachment site in the distal promoter region of a cell cycle-regulated human histone gene. 271 90

Treatment of human HL-60 or KG1A leukemia cells with the topoisomerase II inhibitor etoposide resulted in extensive DNA degradation. When DNA integrity was analyzed by agarose gel electrophoresis, a nucleosomal ladder became evident 1.5-2 h after addition of etoposide to cells, increased in intensity over 6 h, and persisted at 24 h. Six h after addition of the drug, 94 +/- 4% of the cells excluded trypan blue even though as much as 90% of the DNA had been degraded to oligosomal fragments. Exposure of cells to 10 micrograms/ml (17 microM) etoposide for as little as 45 min was sufficient to induce this DNA damage 4 h later. Preincubation with dinitrophenol abolished the effect of etoposide, suggesting that an energy-requiring step occurred prior to or during the endonucleolytic cleavage. In contrast, the effect of etoposide was not prevented by preincubation of HL-60 cells with the RNA synthesis inhibitor 5,6-dichloro-1-beta-ribofuranosylbenzimidazole or the protein synthesis inhibitors cycloheximide or puromycin. On the contrary, high concentrations of 5,6-dichloro-1-beta-ribofuranosylbenzimidazole, cycloheximide, or puromycin by themselves induced the same endonucleolytic cleavage, as did a variety of diverse cytotoxic agents, including camptothecin (0.1 microM), colcemid (0.1 microgram/ml), cis-platinum (20 microM), methotrexate (1 microM), and 1-beta-D-arabinofuranosylcytosine (3 microM). These results suggest that endonucleolytic DNA damage by a preexisting cellular enzyme occurs soon after treatment of HL-60 cells with any of a variety of cytotoxic agents. The observation that a variety of nuclear proteins [including poly(ADP-ribose) polymerase, lamin B, topoisomerase I, topoisomerase II, and histone H1] are degraded concomitant with the DNA fragmentation calls into question the selectivity of the degradative process for DNA. The implications of these results for (a) current theories which focus upon endonucleolytic damage of DNA as a critical early event during cell death, and (b) use of topoisomerase-directed drugs to map topoisomerase-binding sites in active chromatin are discussed.
...
PMID:Induction of endonucleolytic DNA cleavage in human acute myelogenous leukemia cells by etoposide, camptothecin, and other cytotoxic anticancer drugs: a cautionary note. 279 Aug

We have studied the three-dimensional folding of the scaffolding in histone H1-depleted chromosomes by immunofluorescence with an antibody specific for topoisomerase II. Two different types of decondensed chromosomes are observed. The majority of the chromosomes are expanded, and the central fluorescence signal is surrounded by a large halo of chromatin. A much smaller number of chromosomes are more compact in length; they contain a smaller halo of chromatin and their scaffolds are not extended but folded into a genuine, quite regular helical coil. This conclusion is based on a three-dimensional structural analysis by optical sectioning. The number of helical coils is related to chromosome length. Surprisingly, sister chromatids have predominantly opposite helical handedness; that is, they are related by mirror symmetry.
...
PMID:The metaphase scaffold is helically folded: sister chromatids have predominantly opposite helical handedness. 284 11

Nuclear extracts of erythrocytes contain proteins which stably or possibly covalently bind to DNA. These proteins can be detected by an assay which was originally developed to quantify stable binding of topoisomerases to DNA [Trask, DiDonato & Muller (1984) EMBO J. 3, 671-676]. In this report, we show that the number of activities detected by this assay in crude extracts of nuclei is limited predominantly to various forms of topoisomerase I. One form, a 50 kDa protein, copurifies with histone H1. Western blotting experiments suggest that the 50 kDa topoisomerase exists in chromatin along with the 105 kDa form. In addition, the ratio between the high and low-Mr forms is relatively constant in erythrocytes and embryonic fibroblasts. These results imply that the multiple forms are not unique to one tissue setting.
...
PMID:Topoisomerase I is the predominant nuclear protein from avian erythrocytes that can be covalently linked to DNA. 298 49

A DNA topoisomerase activity is found to be associated with the nucleosomes released by the Staphylococcal nuclease digestion of HeLa nuclei. Such an association is found to be salt dependent. A number of criteria have established that this DNA topoisomerase activity is due to HeLa topo I (Liu, L. F. and Miller, K. G. (1980) Proc. Natl. Acad. Sci. USA 78, 3489-3491). A similar association has been demonstrated from the in vitro studies using purified mononucleosomes and eukaryotic DNA topoisomerase I. Nonhistone HMG proteins and histone H1 are found to stimulate topoisomerase activity in vitro and form tight complexes with eukaryotic DNA topoisomerase I. The intimate interactions of topoisomerase I with chromosomal proteins and nucleosomes may be an essential feature of the topoisomerase function in vivo.
...
PMID:Association of eukaryotic DNA topoisomerase I with nucleosomes and chromosomal proteins. 629 26


1 2 3 4 Next >>

---