Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A readily sedimentable nuclear fraction from Chinese hamster embryo fibroblast (CHEF/18) cells catalyzes incorporation of 14C-rCDP into DNA. Data indicated that this incorporation is made possible by the conversion of rCDP into a small and functionally compartmentalized, rather than a large and freely diffusible, pool of dCTP. This catalytically active sedimentable fraction from S phase CHEF/18 cells or actively replicating calf thymus cells contains nascent and template DNA, and numerous enzymes required for DNA biosynthesis including ribonucleoside diphosphate reductase, thymidylate synthetase, dihydrofolate reductase, DNA methylase, topoisomerase and DNA polymerase. We have named this catalytically active macromolecule the replitase. The replitase fraction contained spherical particles with a diameter of approximately 24 to 30 nm and had an estimated molecular weight on the order of 5 X 10(6).
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PMID:Rapid incorporation of label from ribonucleoside disphosphates into DNA by a cell-free high molecular weight fraction from animal cell nuclei. 629 95

At an early purification stage, DNA polymerase alpha holoenzyme from calf thymus can be separated into four different forms by chromatography on DEAE-cellulose. All four enzyme forms (termed A, B, C, and D) are capable of replicating long single-stranded DNA templates, such as parvoviral DNA or primed M13 DNA. Peak A possesses, in addition to the DNA polymerase alpha, a double-stranded DNA-dependent ATPase, as well as DNA topoisomerase type II, 3'-5' exonuclease, and RNase H activity. Peaks B, C, and D all contain, together with DNA polymerase alpha, activities of primase and DNA topoisomerase type II. Furthermore, peak B is enriched in an RNase H, and peaks C and D are enriched in a 3'-5' exonuclease. DNA methylase (DNA methyltransferase) was preferentially identified in peaks C and D. Velocity sedimentation analyses of the four peaks gave evidence of unexpectedly large forms of DNA polymerase alpha (greater than 11.3 s), indicating that copurification of the above putative replication enzymes is not fortuitous. With moderate and high concentrations of salt, enzyme activities cosedimented with DNA polymerase alpha. Peak C is more resistant to inhibition by salt and spermidine than the other three enzyme forms. These results suggest the existence of a leading strand replicase (peak A) and several lagging strand replicase forms (peaks B, C, and D). Finally, the salt-resistant C form might represent a functional DNA polymerase alpha holoenzyme, possibly fitting in a higher-order structure, such as the replisome or even the chromatin.
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PMID:Mammalian DNA polymerase alpha holoenzymes with possible functions at the leading and lagging strand of the replication fork. 658 75

Exposure of human and animal cells to inhibitors of topoisomerase I or II has recently been shown to alter gene expression and induce differentiation in a number of experimental systems. We have previously shown that nalidixic acid and novobiocin, inhibitors of topoisomerase II, induce DNA hypomethylation. Since DNA hypomethylation is frequently associated with transcriptional activation, we wished to further explore the relationship between inhibition of DNA topoisomerases and enzymatic DNA methylation. When HT-29 human colonic adenocarcinoma cells were exposed to the specific topoisomerase II inhibitor teniposide (VM-26), a dose-dependent hypomethylation of DNA was observed during the window of drug treatment. Exposure to the topoisomerase I inhibitor camptothecin (CPT) produced a small but not statistically significant trend toward DNA hypomethylation. CPT-treated cells were found to have up to 19 fold increased levels of topoisomerase II protein, which may have compensated for decreased levels of non-drug-bound topoisomerase I. Both VM-26 and CPT were found to increase [H-3]thymidine incorporation into DNA when administered in low dose (0.5 muM VM-26; 8 nM CPT). Combination of VM-26 and CPT (0.5 muM and 8 nM, respectively) produced DNA hypomethyltion, a synergistic increase in [H-3]thymidine incorporation, and an increasing number of cells entering a higher DNA ploidy cycle. Since VM-26 interferes with the DNA strand breakage-reunion reaction by stabilizing a topoisomerase II-relaxed DNA complex, our results suggest that DNA existing in this form may be a poor substrate for DNA methylase. Topoisomerase inhibitor-induced DNA hypomethylation may offer a possible explanation for the induction of differentiation observed upon exposure to this family of drugs. Altered topoisomerase activity occurring during the process of tumor progression may also provide a link between the induction of polyploidy, DNA hypomethylation and aberrant gene expression frequently observed in tumor cells.
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PMID:Effects of inhibitors of topoisomerases-I and topoisomerases-ii on DNA methylation and DNA-synthesis in human colonic adenocarcinoma cells-invitro. 2158 21

Covalent DNA protein crosslinks (DPCs) are common lesions that block replication. We examine here the consequence of DPCs on mutagenesis involving replicational template-switch reactions in Escherichia coli. 5-Azacytidine (5-azaC) is a potent mutagen for template-switching. This effect is dependent on DNA cytosine methylase (Dcm), implicating the Dcm-DNA covalent complex trapped by 5-azaC as the initiator for mutagenesis. The leading strand of replication is more mutable than the lagging strand, which can be explained by blocks to the replicative helicase and/or fork regression. We find that template-switch mutagenesis induced by 5-azaC does not require double strand break repair via RecABCD; the ability to induce the SOS response is anti-mutagenic. Mutants in recB, but not recA, exhibit high constitutive rates of template-switching, and we suggest that RecBCD-mediated DNA degradation prevents template-switching associated with fork regression. A mutation in the DnaB fork helicase also promotes high levels of template-switching. We also find that other DPC-inducers, formaldehyde (a non-specific crosslinker) and ciprofloxacin (a topoisomerase II poison) are also strong mutagens for template-switching with similar genetic properties. Induction of mutations and genetic rearrangements that occur by template-switching may constitute a previously unrecognized component of the genotoxicity and genetic instability promoted by DPCs.
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PMID:Stimulation of Replication Template-Switching by DNA-Protein Crosslinks. 3059 91