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)

Under some conditions, T4 DNA replication requires the products of the DNA-delay genes, genes 39, 52, 58, and 60. By using an in vitro complementation assay that stimulates DNA replication in T4 39(-)-infected cell extracts, T4 gene 39 protein has been purified. The purified fraction also contains complementing activities for T4 genes 52 and 60. On sodium dodecyl sulfate/polyacrylamide gel analysis the purified preparation exhibits three protein components: a 51,000-dalton protein corresponding to the product of gene 52, a 64,000-dalton protein corresponding to the product of gene 39, and a 110,000-dalton protein. This purified fraction shows a DNA topoisomerase activity that untwists superhelical DNA in an ATP- and Mg2+-dependent reaction. The analogs adenylyl imidodiphosphate and adenyl [beta, gamma-methylene]diphosphonate cannot be used to replace ATP. The topoisomerase activity is not sensitive to the antibiotics oxolinic acid and novobiocin, known antagonists of Escherichia coli DNA gyrase. The possible relationship among the three polypeptides and their biological activities is discussed.
...
PMID:T4 DNA-delay proteins, required for specific DNA replication, form a complex that has ATP-dependent DNA topoisomerase activity. 22 76

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.
...
PMID:A topoisomerase from Escherichia coli related to DNA gyrase. 23 Apr 98

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

We have investigated the amount of DNA topoisomerase II and phosphorylation of the enzyme in Swiss 3T3 cells during the transition from cell quiescence to proliferation. A relatively high level of phosphorylation was observed with proliferating cells while no or a very low level of phosphorylation was observed with quiescent cells. Phosphoamino acid analysis of the phosphorylated topoisomerase II revealed that the phosphorylated aminoacyl residue was serine. When quiescent cells were stimulated to grow by the addition of serum, DNA synthesis began to increase at 9 h after serum addition, reaching a maximum at 15 h and then declining. The amount of topoisomerase II began to increase at 6 h and reached a maximum at 22-27 h, corresponding to the G2 phase. The phosphorylation of topoisomerase II measured by pulse-labeling gradually increased from 6 to 18 h and reached a maximum at 22 h when the amount of the enzyme was maximum. The level of phosphorylation measured by continuous-labeling increased gradually up to 12 h and markedly up to 28 h, and then declined. The increase in the rate of phosphorylation in the G2 phase was affected by inhibiting DNA synthesis, but the increase in the amount of the enzyme was not. Thus, it was suggested that the regulation of phosphorylation of topoisomerase II differs from that of the amount of the enzyme.
...
PMID:Growth state and cell cycle dependent phosphorylation of DNA topoisomerase II in Swiss 3T3 cells. 131 36

Cloning and sequencing of cDNA segments of human TOP2 gene encoding the 170 kDa form of human DNA topoisomerase II show that Arg486 of the enzyme has been mutated to a lysine in the enzyme from two human leukemia cell lines HL-60/AMSA and KBM-3/AMSA, which were independently selected for resistance to the antitumor drug amsacrine (4'-[9-acridinylamino]-methanesulfon-m-anisidide, mAMSA). Sequence identity comparisons between eukaryotic DNA topoisomerase II and bacterial gyrase (bacterial DNA topoisomerase II) indicate that the position of the common mutation observed in mAMSA-resistant human TOP2 corresponds to that of the point mutation nal-31 in the Escherichia coli gyrase B gene, which confers resistance to nalidixic acid. Because mAMSA and nalidixic acid are known to act on their respective targets by a common mechanism of trapping the covalent enzyme-DNA intermediates, these results provide strong evidence that the 170 kDa form of human DNA topoisomerase II is a major cellular target of mAMSA, and that Arg486 of this enzyme is involved in mAMSA-mediated trapping of the covalent enzyme-DNA complex.
...
PMID:Two independent amsacrine-resistant human myeloid leukemia cell lines share an identical point mutation in the 170 kDa form of human topoisomerase II. 131 90

The 2'-chloro derivatives of etoposide and 4 beta-(arylamino)-4'-O-demethylpodophyllotoxins have been synthesized and evaluated for their inhibitory activity against the human DNA topoisomerase II as well as for their activity in causing cellular protein-linked DNA breakage. The results showed that none of the compounds are active as a result of the C-2' chloro substitution on ring E. This would suggest that the free rotation of ring E is essential for the aforementioned enzyme inhibitory activity. In addition, these 2'-chloro derivatives showed no significant cytotoxicity (KB).
...
PMID:Antitumor agents. 123. Synthesis and human DNA topoisomerase II inhibitory activity of 2'-chloro derivatives of etoposide and 4 beta-(arylamino)-4'-O-demethylpodophyllotoxins. 131

A series of 6,7-O,O-demethylene-4'-O-demethyl-4 beta-(substituted anilino)-4-desoxypodophyllotoxins (18-23), 6,7-O,O-demethylene-6,7-O,O-dimethyl-4'-O-demethyl-4 beta-(substituted anilino)-4-desoxypodophyllotoxins (28-31), and their corresponding 4'-O-methyl analogues (12-17 and 24-27) have been synthesized and evaluated for their inhibitory activity against the human DNA topoisomerase II as well as for their activity in causing cellular protein-linked DNA breakage. Compounds 18-23 are 2-fold more potent than etoposide and compounds 12, 16, 17, 30, and 31 are as active as etoposide in their inhibition of the human DNA topoisomerase II. Compounds 19 and 20 and 29-31 are as active or more active than etoposide in causing protein-linked DNA breakage. These results indicate that a free C-4' hydroxy group is essential for the DNA breakage activity, and that the hydroxyl groups at C-6 and -7 positions may be involved in an interaction which is responsible for the inhibitory activity of DNA topoisomerase II. The maintenance of an intact methylene dioxy-type ring-A system would contribute to enhanced activity. In addition, the sterically less hindered substitution at C-6 and C-7 positions may be important for optimal interactions with DNA topoisomerase II. There is no correlation between the ability of these compounds to inhibit DNA topoisomerase II and their ability to cause protein-linked DNA breaks in cells. This may relate to the difference in uptake of these compounds. The better correlation was observed between the protein-linked DNA breaks and the cytotoxicity in KB cells of these compounds.
...
PMID:Antitumor agents. 124. New 4 beta-substituted aniline derivatives of 6,7-O,O-demethylene-4'-O-demethylpodophyllotoxin and related compounds as potent inhibitors of human DNA topoisomerase II. 131 1

The antitrypanosomal and antifiliarial drug suramin is currently under investigation for treatment of advanced malignancies including prostatic cancer, adrenocortical cancer, and some lymphomas and sarcomas. Here we show that suramin is a potent inhibitor of the nuclear enzyme DNA topoisomerase II. Suramin inhibited purified yeast topoisomerase II with an IC50 of about 5 microM, as measured by decatenation or relaxation assays. Suramin did not stabilize the covalent DNA-topoisomerase II reaction intermediate ("cleavable complex"), whereas other inhibitors of this enzyme, such as amsacrine, etoposide, and the ellipticines, are known to stabilize the intermediate. In contrast, the presence of suramin strongly inhibited the cleavable-complex formation induced by amsacrine or etoposide. Accumulation of the endogenous cleavable complex was also inhibited. Suramin entered the nucleus of DC-3F Chinese hamster fibrosarcoma cells exposed to radiolabeled suramin for 24 hr as shown by both optic and electron microscopy. The suramin present in the nucleus seemed to interact with topoisomerase II, since suramin reduced the number of amsacrine-induced protein-associated DNA strand breaks in DC-3F cells and protected these cells from the cytotoxic action of amsacrine. Cells resistant to 9-hydroxyellipticine, which have been shown to have an altered topoisomerase II activity, are about 7-fold more resistant to suramin than the sensitive parental cells as shown by 72-hr growth inhibition assay. Our results suggest that DNA topoisomerase II is a target of suramin action and that this action may play a role in the cytotoxic activity of suramin.
...
PMID:Suramin is an inhibitor of DNA topoisomerase II in vitro and in Chinese hamster fibrosarcoma cells. 131 77

Several monoclonal antibodies of different isotypes specific to human DNA topoisomerase I, to 170- and 180-kDa DNA topoisomerase II isozymes, were produced and characterized. The specificity of monoclonal antibodies was confirmed by comparison with polyclonal antibodies by Western blot, by immunoprecipitation of enzyme activity, and by immunoprecipitation of DNA topoisomerases with characterized polyclonal antisera. Morphological studies performed by immunofluorescence indicate that the three groups of monoclonal antibodies (MoAbs) stain the nucleus with characteristic patterns, which can be compared with those obtained with polyclonal antibodies. In particular the MoAbs to the 100-kDa DNA topoisomerase I stain the nucleolus and the nucleoplasm; the MoAbs to 170- and 180-kDa DNA topoisomerase II give completely distinct intranuclear patterns: those to the 170-kDa protein stain mainly the nucleoplasm, whereas those to the 180-kDa protein stain only the nucleolus. The two DNA topoisomerase II isozymes clearly exhibit fluctuations in their expression during cell growth: the 170-kDa isozyme is more abundant during the logarithmic phase of growth, while the 180-kDa isozyme is mainly present during the plateau phase of growth.
...
PMID:Monoclonal antibodies to human DNA topoisomerase I and the two isoforms of DNA topoisomerase II: 170- and 180-kDa isozymes. 131 88

Monoclonal antibodies raised against two isoforms (170 and 150/180 kDa) of DNA topoisomerase II showed distinct fluorescence patterns in HeLa cells in different moments of the cell cycle (C. Negri et al., 1992, Exp. Cell Res. 200, 452-459). The ultrastructural distribution of the 150/180-kDa isoform, which in immunofluorescence showed a localization into the nucleolar region, has been analyzed by electron microscopy with a gold-conjugated secondary antibody in HeLa and K562 cells. The results indicate that this isoform of the enzyme is exclusively localized in the nucleolus, mainly in the dense fibrillar component, while the nucleoplasm of interphase cells and the chromosomes of mitotic cells are completely negative. The antibody also reacts with the nucleolus of isolated nuclei and with the nucleolar remnant of purified nuclear matrices. A quantitative evaluation of the label distribution indicates that the percentage of label in the nucleolar remnant of isolated matrix is almost identical to that of the nucleolus in whole cells. The interaction with the insoluble proteins of the isolated nuclear matrix is also demonstrated by quantitative immunoblotting in which the MoAb specifically stains a unique band corresponding to the 150/180-kDa isoform of topoisomerase II. The localization of the 150/180-kDa isoform of topoisomerase II in the nucleolar remnant strongly suggests that it represents a structural element for the spatial organization and for the regulation of transcription of the ribosomal genes.
...
PMID:The 180-kDa isoform of topoisomerase II is localized in the nucleolus and belongs to the structural elements of the nucleolar remnant. 131 89


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

---