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:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The incubation of the E coli DNA binding protein HU with relaxed circular SV40 DNA in the presence of pure nicking-closing enzyme introduces up to 18 negative superhelical turns in the DNA molecules as measured by agarose gel electrophoresis. The maximal density of supercoiling is obtained at a HU-DNA mass ratio of 1. Reconstituted DNA-HU complexes prefixed with glutaraldehyde appear as condensed circular structures having an average of 14 "beads" per circular SV40 DNA molecule, with a "bead" diameter of 180 +/- 23 A. The circular SV40 DNA is condensed by a ratio of 2.0-2.5 relative to naked DNA. This is similar to the ratio (2.4) measured for chromatin formed by reassociation of relaxed SV40 DNA with the four core histones.
...
PMID:E. coli DNA binding protein HU forms nucleosomelike structure with circular double-stranded DNA. 22 78

Purified vaccinia virus DNA topoisomerase I forms a cleavable complex with duplex DNA at a conserved sequence element 5'(C/T)CCTTdecreases in the incised DNA strand. DNase I footprint studies show that vaccinia topoisomerase protects the region around the site of covalent adduct formation from nuclease digestion. On the cleaved DNA strand, the protected region extends from +13 to -13 (+1 being the site of cleavage). On the noncleaved strand, the protected region extends from +13 to -9. Similar nuclease protection is observed for a mutant topoisomerase (containing a Tyr ---- Phe substitution at the active site amino acid 274) that is catalytically inert and does not form the covalent intermediate. Thus, vaccinia topoisomerase is a specific DNA binding protein independent of its competence in transesterification. By studying the cleavage of a series of 12-mer DNA duplexes in which the position of the CCCTTdecreases motif within the substrate is systematically phased, the "minimal" substrate for cleavage has been defined; cleavage requires six nucleotides upstream of the cleavage site and two nucleotides downstream of the site. An analysis of the cleavage of oligomer substrates mutated singly in the CCCTT sequence reveals a hierarchy of mutational effects based on position within the pentamer motif and the nature of the sequence alteration.
...
PMID:Site-specific interaction of vaccinia virus topoisomerase I with duplex DNA. Minimal DNA substrate for strand cleavage in vitro. 168 12

A number of characteristics in the human genetic disorder ataxia-telangiectasia are compatible with an alteration to chromatin structure or the recognition of that structure by an enzyme or DNA binding protein. We describe here reduce activity of DNA topoisomerase type II in a number of Epstein Barr Virus-transformed ataxia-telangiectasia lymphoblastoid cell lines. Enzyme activity was reduced 10-fold or greater in 4 out of 5 cell lines compared to controls. In the remaining cell line approximately a 2-3 fold reduction was evident in partially purified extracts. DNA topoisomerase type I activity was found to be the same as controls in all the cell lines. Northern blot analysis revealed that the same level of DNA topoisomerase II mRNA was expressed in ataxia-telangiectasia and control cell lines. The size and amount of the enzyme did not differ appreciably from that observed in control cells. The reduced activity of DNA topoisomerase II in ataxia-telangiectasis cells might be explained by amino acid substitutions, small deletions in DNA or by a defect in post-translational modification in these cells.
...
PMID:Defective DNA topoisomerase II in ataxia-telangiectasia cells. 196 59

We have identified DNA fragments which bind specifically to the nuclear matrix in vitro, termed matrix association regions (MARs), in the first and fourth introns of rat alpha 2-macroglobulin gene. The MAR in the first intron is enriched with sequences closely related to the cleavage consensus of topoisomerase II, and contains the binding site of nuclear factor-alpha, a sequence-specific DNA binding protein reported previously.
...
PMID:Nuclear matrix association regions of rat alpha 2-macroglobulin gene. 244 78

The human single-stranded-DNA binding protein (human SSB) is required for simian virus 40 (SV40) DNA replication in vitro. SV40 large tumor antigen and human SSB can support extensive unwinding of SV40 origin-containing DNA in the presence of ATP and a topoisomerase that relieves positive superhelicity. Although SSBs from viral and prokaryotic sources substituted for human SSB in the DNA-unwinding reaction, they did not substitute in the replication of SV40 DNA. The specificity for human SSB in SV40 DNA replication can be explained, at least in part, by the finding that DNA polymerase alpha was stimulated 10-fold by human SSB but not by other SSBs. Human SSB also stimulated proliferating-cell nuclear antigen-dependent DNA polymerase delta; however, other SSBs stimulated this polymerase as well.
...
PMID:Multiple functions of human single-stranded-DNA binding protein in simian virus 40 DNA replication: single-strand stabilization and stimulation of DNA polymerases alpha and delta. 255 26

The replication of DNA containing either the polyoma or SV40 origin has been done in vitro. Each system requires its cognate large-tumour antigen (T antigen) and extracts from cells that support its replication in vivo. The host-cell source of DNA polymerase alpha - primase complex plays an important role in discriminating between polyoma T antigen and SV40 T antigen-dependent replication of their homologous DNA. The SV40 origin- and T antigen-dependent DNA replication has been reconstituted in vitro with purified protein components isolated from HeLa cells. In addition to SV40 T antigen, HeLa DNA polymerase alpha - primase complex, eukaryotic topoisomerase I and a single-strand DNA binding protein from HeLa cells are required. The latter activity, isolated solely by its ability to support SV40 DNA replication, sediments and copurifies with two major protein species of 72 and 76 kDa. Although crude fractions yielded closed circular monomer products, the purified system does not. However, the addition of crude fractions to the purified system resulted in the formation of replicative form I (RFI) products. We have separated the replication reaction with purified components into multiple steps. In an early step, T antigen in conjunction with a eukaryotic topoisomerase (or DNA gyrase) and a DNA binding protein, catalyses the conversion of a circular duplex DNA molecule containing the SV40 origin to a highly underwound covalently closed circle. This reaction requires the action of a helicase activity and the SV40 T antigen preparation contains such an activity. The T antigen associated ability to unwind DNA copurified with other activities intrinsic to T antigen (ability to support replication of SV40 DNA containing the SV40 origin, poly dT-stimulated ATPase activity and DNA helicase).
...
PMID:In vitro replication of DNA containing either the SV40 or the polyoma origin. 289 81

The simian virus 40 (SV40) large T antigen (large tumor antigen), in conjunction with a topoisomerase, a DNA binding protein, and ATP, catalyzed the conversion of a circular duplex DNA molecule containing the SV40 origin of replication to a form with unusual electrophoretic mobility that we have named form U. Analysis of this molecule revealed it to be a highly underwound covalently closed circle. DNA unwinding was not detected with DNA containing a SV40 T-antigen binding site II mutation that renders the DNA inactive in replication. The unwinding reaction requires the action of a helicase, and SV40 T-antigen preparations contain such an activity. The T-antigen-associated ability to unwind DNA copurified with other activities intrinsic to T antigen [ability to support replication of SV40 DNA containing the SV40 origin, poly(dT)-stimulated ATPase activity, and DNA helicase]. However, in contrast to the unwinding activity, the SV40 T-antigen-associated helicase activity was not sequence-specific. A variety of labeled oligonucleotides hybridized with circular single-stranded DNA were displaced by T antigen in the presence of ATP.
...
PMID:Simian virus 40 (SV40) DNA replication: SV40 large T antigen unwinds DNA containing the SV40 origin of replication. 302 51

Crithidia fasciculata DNA topoisomerase (22) has been purified to near homogeneity from trypanosomatid cell extracts. The purified enzyme catalyzes the reversible interconversion of monomeric duplex DNA circles and catenanes in an ATP dependent reaction. Reversible catenane formation is affected by the ionic strength and is dependent upon the action of a crithidial DNA binding protein, which could be substituted for the polyamine spermidine. Covalently sealed DNA circles are specifically used as substrates for decatenation. Nicking, but not relaxation per se, inhibits network decatenation and has little or no effect on catenane formation. The catalytic properties of this enzyme and its potential role in the prereplication release and post replication reattachment of kDNA minicircles are discussed.
...
PMID:A unique ATP-dependent DNA topoisomerase from trypanosomatids. 609 60

As shown by competition experiments, the single-strand DNA binding protein from normal rat liver (S25) interacts preferentially with supercoiled DNA compared to relaxed DNA duplexes. When followed both by sedimentation analysis and by nitrocellulose filter assay, the binding of S25 to SV40 supercoiled DNA (FI) appears to be non-cooperative. Saturation is reached at a protein to DNA weight ratio of about 2. The S25-DNA complexes prefixed with glutaraldehyde appear as beaded structures having an average of 14 to 16 beads per SV40 DNA molecules. Cross-linking of S25 bound to SV40 DNA by dimethyl suberimidate allows to detect oligomeric structures containing a maximum of twenty monomers of S25. When complexes are treated by glutaraldehyde, 10% of the genome become resistant against micrococcal nuclease. Moreover, S25 affects the DNA helical structure. Superhelical forms are generated by the association of S25 with SV40 DNA, in the presence of nicking-closing enzyme.
...
PMID:Single-strand DNA binding protein from rat liver: interactions with supercoiled DNA. 625 39

A protein required for the elongation of replicating intermediates of adenovirus (Ad) DNA to full length has been isolated and characterized. This factor, isolated from nuclear extracts of uninfected HeLa cells, has been designated nuclear factor II. In the presence of Ad DNA with proteins at each 5' end (Ad DNA-protein) and three proteins coded for by the Ad genome [the preterminal protein (pTP), the DNA polymerase (Ad Pol), and the DNA binding protein (Ad DBP)], nuclear factor II complementing activity is detected only in the presence of host nuclear factor I. Highly purified preparations of nuclear factor II that are free of detectable DNA polymerase alpha, beta, and gamma activities contain a DNA topoisomerase activity. Furthermore, type I DNA topoisomerases purified from HeLa cells and calf thymus substitute for nuclear factor II complementing activity in the in vitro Ad DNA replication system. These results indicate that a protein that is involved in higher order DNA structure is required for Ad replication. This protein plus the purified proteins described above carry out the initiation and synthesis of full-length 36,000-base-pair Ad DNA.
...
PMID:Adenovirus DNA replication in vitro: synthesis of full-length DNA with purified proteins. 630 11


1 2 3 Next >>

---