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

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

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).
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PMID:In vitro replication of DNA containing either the SV40 or the polyoma origin. 289 81

DNA-dependent ATPase IV has been purified to near homogeneity from the Novikoff rat hepatoma. The enzyme is devoid of DNA polymerase, RNA polymerase, exonuclease, endonuclease, phosphomonoesterase, 3'- or 5'-phosphodiesterase, polynucleotide kinase, protein kinase, topoisomerase, helicase or DNA reannealing activities at a detection level of 10(-5) to 10(-7) relative to the ATPase activity. The enzyme is a monomer of Mr 110,000, has a sedimentation coefficient of 5.9 S, a Stokes radius of 40 A and a frictional coefficient of 1.32. In the presence of Mg2+ ion and a polynucleotide effector, ATPase IV hydrolyzes either ATP or dATP to the nucleoside diphosphate plus Pi. Other ribo- or deoxyribonucleoside triphosphates are not substrates. ATPase IV utilizes double-stranded DNA and single-stranded DNA as effector; however, it does not utilize poly(dT). The Km for dsDNA or ssDNA is 2.2 microM (nucleotide). A variety of ATP analogues were found to be competitive inhibitors of ATPase IV.
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PMID:Purification and enzymological characterization of DNA-dependent ATPase IV from the Novikoff hepatoma. 296 5

We report here the large scale purification of DNA topoisomerase II from calf thymus glands, using the unknotting of naturally knotted P4 phage DNA as an assay for enzymatic activity. Topoisomerase II was purified more than 1300-fold as compared to the whole cell homogenate, with 22% yield. Analysis of the purified enzyme by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed two bands of apparent molecular masses of 125 and 140 kDa. Tryptic maps of the two bands indicated that they derive from the same protein. Using these fragments, specific polyclonal antisera to topoisomerase II were raised in rabbits. Immunoblotting of whole cell lysates from various species indicated that topoisomerase II is well conserved among mammals and has a native subunit molecular mass of 180 kDa. Analytical sedimentation and gel filtration were used to determine a sedimentation coefficient of 9.8 S and a Stokes radius of 68 A. The calculated solution molecular mass of 277 kDa implies a dimer structure in solution. The purified topoisomerase II unknots P4 DNA in an ATP-dependent manner and is highly stimulated in its relaxation activity by ATP. A DNA-stimulated ATPase activity, as has been found with other type II topoisomerases, is associated with the purified enzyme. Approximate kinetic parameters for the ATPase reaction were determined to be: a Vmax of 0.06 nmol of ATP/(micrograms of protein) (min) and Km of 0.2 mM in the absence of DNA, and a Vmax of 0.2 nmol of ATP/(micrograms of protein) (min) and Km of 0.4 mM ATP in the presence of supercoiled plasmid DNA.
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PMID:Purification and characterization of a type II DNA topoisomerase from bovine calf thymus. 298 21

Type I topoisomerases have been purified from nuclei and mitochondria of human acute lymphoblastic leukemia cells. Both of these ATP-independent enzymes are actually found to be inhibited by ATP at physiologically significant concentrations. Other adenine nucleotides showed varying effects: ADP inhibited only at high concentrations; AMP had no effect on either topoisomerase. Both enzymes were also inhibited by dATP. The importance of the adenine ring structure was confirmed by the lack of an inhibitory effect observed with equivalent levels of GTP, UTP, CTP, or their deoxy counterparts. Assays performed in the presence of nonhydrolyzable analogs of ATP suggest that hydrolysis of ATP does not accompany this enzyme inhibition. This was supported by direct determination of the ATPase activity of the purified enzymes. Type I topoisomerase from calf thymus and HeLa cells were also found to be sensitive to ATP. These results suggest that mammalian type I topoisomerases in general may possess a nucleotide-binding site that may be involved in regulation of enzyme activity.
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PMID:ATP inhibits nuclear and mitochondrial type I topoisomerases from human leukemia cells. 300 64

We have characterized in Trypanosoma cruzi a DNA topoisomerase capable of decatenating complex trypanosomal kinetoplast DNA networks in the absence of ATP. The enzymatic activity requires Mg2+ and K+. Using a defined DNA topoisomer we showed that the linking number changes by steps of 2, which characterizes the enzyme as a type II topoisomerase. The enzyme can catenate supercoiled DNA molecules, unknot DNA, and cleave double-stranded DNA. The enzyme has no ATPase activity. The native enzyme has an Mr of about 200,000. Crude extracts and partially purified fractions contain an aggregating factor that can substitute spermidine in catenating reactions. Because of the presence of this factor, the kinetoplast DNA can only be decatenated by purified fractions. The enzyme is inhibited by certain drugs and provides a potential target for chemotherapy. Such an enzyme was also characterized in Trypanosoma equiperdum.
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PMID:ATP-independent type II topoisomerase from trypanosomes. 302 May 37

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.
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PMID:Simian virus 40 (SV40) DNA replication: SV40 large T antigen unwinds DNA containing the SV40 origin of replication. 302 51

A high-molecular-weight protein complex that is capable of accurate transcription initiation and termination of vaccinia virus early genes without additional factors was demonstrated. The complex was solubilized by disruption of purified virions, freed of DNA by passage through a DEAE-cellulose column, and isolated by glycerol gradient sedimentation. All detectable RNA polymerase activity was associated with the transcription complex, whereas the majority of enzymes released from virus cores including mRNA (nucleoside-2'-O)methyltransferase, poly(A) polymerase, topoisomerase, nucleoside triphosphate phosphohydrolase II, protein kinase, and single-strand DNase sedimented more slowly. Activities corresponding to two enzymes, mRNA guanylyltransferase (capping enzyme) and nucleoside triphosphate phosphohydrolase I (DNA-dependent ATPase), partially sedimented with the complex. Silver-stained polyacrylamide gels, immunoblots, and autoradiographs confirmed the presence of subunits of vaccinia virus RNA polymerase, mRNA guanylyltransferase, and nucleoside triphosphate phosphohydrolase I, as well as additional unidentified polypeptides, in fractions with transcriptase activity. A possible role for the DNA-dependent ATPase was suggested by studies with ATP analogs with gamma-S or nonhydrolyzable beta-gamma-phosphodiester bonds. These analogs were used by vaccinia virus RNA polymerase to nonspecifically transcribe single-stranded DNA templates but did not support accurate transcription of early genes by the complex. Transcription also was sensitive to high concentrations of novobiocin; however, this effect could be attributed to inhibition of RNA polymerase or ATPase activities rather than topoisomerase.
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PMID:Sedimentation of an RNA polymerase complex from vaccinia virus that specifically initiates and terminates transcription. 303 83

Reverse gyrase is a type I DNA topoisomerase that promotes positive supercoiling of closed-circular double-stranded DNA through an ATP-dependent reaction, and it was purified from an archaebacterium, Sulfolobus. When ATP is replaced by UTP, GTP, or CTP, this enzyme just relaxes the negatively supercoiled closed-circular double-stranded DNA. We found that reverse gyrase hydrolyzes ATP through a double-stranded DNA-dependent reaction. The superhelicity of the DNA did not affect the ATPase activity. However, reverse gyrase does not hydrolyze UTP, GTP, or CTP. Therefore, any of the four nucleotide 5'-triphosphates acts as an effector for the topoisomerase activity of reverse gyrase, but only ATP supports the positive supercoiling of closed-circular double-stranded DNA, through the energy released on its hydrolysis. Single-stranded DNA was a much more potent cofactor for the ATPase activity of the enzyme than double-stranded DNA, and it acted as a potent inhibitor for the topoisomerase activity on double-stranded DNA. These results indicate that reverse gyrase has higher affinity to single-stranded DNA than to double-stranded DNA, which suggests a cellular function of the enzyme.
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PMID:Intrinsic DNA-dependent ATPase activity of reverse gyrase. 303 79

A DNA ligase has been purified approximately 2,100-fold, to near-homogeneity, from Drosophila melanogaster 6-12-h embryos and was shown to catalyze the formation of 3',5'-phosphodiester bonds. Polypeptides with molecular weights 83,000, 75,000, and 64,000 were observed when the purified enzyme was electrophoresed under denaturing conditions. These polypeptides were shown by partial proteolysis studies and two-dimensional gel analysis to be structurally related. The two smaller polypeptides were presumably derived from the largest, 83,000 molecular weight protein, by proteolysis during purification or in vivo. All three polypeptides formed enzyme-adenylylate complexes in the absence of DNA. Drosophila DNA ligase had a Stokes radius of 45 A, a sedimentation coefficient of 4.3 S, and a frictional ratio of 1.6, yielding a calculated molecular weight of 79,800. These studies indicate that DNA ligase from Drosophila embryos is a monomer. The purified ligase was free of detectable ATPase, nuclease, topoisomerase, and DNA polymerase activities. The enzyme exhibited an absolute requirement for ATP in the joining reaction. A divalent metal was required and N-ethylmaleimide inhibited the reaction. Formation of phosphodiester bonds by Drosophila ligase required the presence of 5'-phosphoryl and 3'-hydroxyl termini. The purified enzyme restored biological activity to endonucleolytically cleaved pBR322 DNA. The specific activity of Drosophila DNA ligase was highest in unfertilized eggs. Developing embryos had 5-10-fold more ligase activity than at any later time in development.
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PMID:DNA ligase from Drosophila melanogaster embryos. Purification and physical characterization. 309 38

Using kinetoplast DNA networks as a substrate in a decatenation assay, we have purified to apparent homogeneity a type II DNA topoisomerase from HeLa cell nuclei. The most pure preparations contain a single polypeptide of 172,000 daltons as determined by sodium dodecyl sulfate-gel electrophoresis. The molecular weight of the native protein, based on sedimentation and gel filtration analyses, is estimated to be 309,000. These results suggest that the enzyme is a dimer of 172,0090-dalton subunits. The enzyme is a type II topoisomerase as demonstrated by its ability to change the linking number of DNA circles in steps of two and to decatenate or unknot covalently closed DNA circles. No gyrase activity is detectable. ATP is required for the relaxation, decatenation, and unknotting of DNA, and a DNA-dependent ATPase activity is present in the most pure fractions. ATP is hydrolyzed to ADP in this properties to T4 DNA topoisomerase (Liu, L. F., Liu, C. C., and Alberts, B. M. (1979) Nature 281, 456-461).
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PMID:A homogeneous type II DNA topoisomerase from HeLa cell nuclei. 626 71


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