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:2.1.1.37 (DNA methyltransferase)
4,983 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Parallel studies were performed with methionineless derivatives of Escherichia coli 15 T(-) and Bacillus megaterium KM: T(-). Methylated bases are present in the total cell ribonucleic acid (RNA) of B. megaterium. The level of RNA methylation in E. coli is about 60% greater than that in B. megaterium. Although E. coli deoxyribonucleic acid (DNA) was found to contain 0.12% 5-methylcytosine (5-MC) and 0.24% 6-methylaminopurine (6-MA), methylated bases were not detected in the DNA of B. megaterium. Assuming a molecular weight of 7 x 10(9) daltons for B. megaterium DNA, it was calculated that this organism could not contain more than one molecule of 5-MC or 6-MA per genome, and that possibly no methylated bases were present. Methylated bases were also not detected in the DNA of thymine-starved B. megaterium. Crude extracts of this organism possess RNA methylase activity but no detectable DNA methylase activity.
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PMID:Methylated bases of Bacillus megaterium KM nucleic acids: comparison with Escherichia coli. 499 70

Deoxyribonucleic acid methylase activity has been detected in a preparation of disrupted nuclei prepared from pea seedlings. S-Adenosyl-L-methionine acted as a donor of methyl groups, and the product of the reaction was identified as 5-methylcytosine. The reaction had a sharp temperature optimum at about 30 degrees C and was unusual in that the DNA methylase was able to methylate DNA in the crude extract.
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PMID:Deoxyribonucleic acid methylase activity in pea seedlings. 577 22

Using enzymatic modelling of in vitro methylation of chromosome DNAs from Yersinia pestis EV 76, E. coli 834 and E. coli C600 RII by DNA methylases of Eco RII and Eco dam as well as of DNA hydrolysis of plasmid pBR 322 from the cells of Y. pestis EV 76, E. coli C600 and E. coli 834 by restrictases of Eco RII and Cfu I, it was found that cytosine DNA methylase from plague bacteria does not correspond to the type of RII methylases of E. coli. Adenyl DNA methylase is related to E. coli methylases type dam and modifies adenine in the nucleotide sequence of GATC.
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PMID:[Comparison of specific recognition sites of adenine and cytosine DNA-methylase of Yersinia Pestis EV 76 C dam and dcm by Escherichia coli methylases]. 609 1

5-Azacytidine inhibited in vivo DNA methylation in Ehrlich's ascites tumor cells depending upon the dose at which 5-azacytidine did not inhibit DNA synthesis significantly. This drug did not inhibit DNA methylation in vitro. The DNA methylase activity in ascitic cells decreased with the increasing dose of 5-azacytidine. Hypomethylated DNA was obtained from the 5-azacytidine treated ascitic cells.
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PMID:Effect of 5-azacytidine on DNA methylation in Ehrlich's ascites tumor cells. 615 82

In order to understand further the molecular mode of action of 5-Aza-2'-deoxycytidine (5-AZA-dCyd), a potent antileukemic agent, we prepared enzymatically 5-Aza-2'-deoxycytidine 5'-triphosphate (5-AZA-dCTP) and performed studies with purified DNA polymerase alpha and DNA methylase from mammalian cells. DNA polymerase alpha catalyzed the incorporation of 5-AZA-dCTP into DNA. The apparent Km value for 5-AZA-dCTP was estimated to be 3.0 microM; the Km of dCTP was 2.0 microM. The apparent Vmax of 5-AZA-dCTP was slightly lower than that for dCTP. 5-AZA-dCTP was a weak competitive inhibitor (Ki 4.3 microM) with respect to dCTP. Template studies with 5-AZA-dCTP showed that this nucleotide analogue was incorporated into poly(dIC), but not into poly(dAT), suggesting that the incorporation follows the rules of Watson-Crick base pairing. Incorporation of 5-AZA-dCTP into hemimethylated DNA produced a significant inhibition of DNA methylase. These results show that 5-AZA-dCTP is a very good substrate for DNA polymerase alpha and that its incorporation into DNA inhibits DNA methylation.
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PMID:Incorporation of 5-Aza-2'-deoxycytidine-5'-triphosphate into DNA. Interactions with mammalian DNA polymerase alpha and DNA methylase. 619 Nov 92

A partially purified HeLa cell DNA methylase will methylate a totally unmethylated DNA (de novo methylation) at about 3-4% the rate it will methylate a hemimethylated DNA template (maintenance methylation). Our evidence suggests that many, if not most, dCpdG sequences in a natural or synthetic DNA can be methylated by the enzyme. There is a powerful inhibitor of DNA methylase activity in crude extracts which has been identified as RNA. The inhibition of DNA methylase by RNA may indicate that this enzyme is regulated in vivo by the presence of RNA at specific chromosomal sites. The pattern of binding of RNA to DNA in the nucleosome structure and the DNA replication complex may determine specific sites of DNA methylation. An even more potent inhibition of DNA methylase activity is observed with poly(G), but not poly(C), poly(A), or poly(U). The only other synthetic polynucleotides studied which inhibit DNA methylation as well as poly(G) are the homopolymers poly(dC).poly(dG) and poly (dA).poly(dT). These results point out the unique importance of the guanine residue itself in the binding of the DNA methylase to dCpdG, the site of cytosine methylation. The surprising inhibition of the methylation reaction by poly(dA).poly(dT), which is itself not methylated by the enzyme, suggests the possible involvement of adjacent A and T residues in influencing the choice of sites of methylation by the enzyme.
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PMID:DNA methylation. Inhibition of de novo and maintenance methylation in vitro by RNA and synthetic polynucleotides. 620 88

We have previously shown that treatment of normal and neoplastic cells with the antileukemic drug, 5-azacytidine, led to the rapid synthesis of a low molecular weight RNA containing 5-azacytosine. This fraudulent RNA inhibited tRNA (cytosine-5)-methyltransferase early after drug administration. The absence of tRNA (cytosine-5)-methyltransferase activity resulted in the synthesis of tRNA specifically deficient in 5-methylcytosine. Here, we show that treatment of L1210 cells, grown intraperitoneally in mice, with 5-azacytidine led to a rapid and prolonged inactivation of DNA (cytosine-5)-methyltransferase activity and to the synthesis of undermethylated DNA. DNA isolated from the treated tissue was found to inactivate the DNA methylase (decreased Vmax) in in vitro DNA (cytosine-5)-methyltransferase assays. Kinetic analysis showed noncompetitive inhibition of the substrate by the inhibitor. The persistence of DNA undermethylation after treatment with 5-azadeoxycytidine or 5-azacytidine in animals has not been measured directly; therefore, we have investigated this phenomenon in the intact animal. Prolonged treatment with 5-azacytidine was required to maintain a a fraction of undermethylated sites in DNA of L1210 cells in vivo for up to 4 months or longer after drug withdrawal. Such treatment led to instability of DNA methylation levels in L1210 cells in vivo. At least a partial restoration of DNA 5-methylcytosine levels was observed after acute and chronic 5-azacytidine treatment, respectively. 5-Azacytidine was also found to induce DNA hypomethylation in regenerating, but not in normal adult mouse liver cells. Our results show that: 1) it was extremely difficult to decrease the DNA methylation level to less than 50% of control; and 2) it was also difficult to maintain stable DNA methylation levels in vivo after exposure to the drug.
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PMID:Long term instability and molecular mechanism of 5-azacytidine-induced DNA hypomethylation in normal and neoplastic tissues in vivo. 620 75

The status of DNA methylation, as measured by the 5-methylcytosine content of nuclear DNA, was examined in normal livers and in chemically induced or spontaneous primary hepatocellular carcinoma (PHC) arising in three strains of mice. The DNA from spontaneous tumors of genetic origin in C3H mice and also from acetylaminofluorene, chlordane, or 3'-methyl-4-dimethylaminoazobenzene-induced tumors in C57Bl and B6C3 mice was undermethylated compared to the levels in background and normal liver samples. The DNA methylase activities from normal liver, background liver, and PHC were assayed in C3H mice to determine whether the observed genomic undermethylation is related to a dysfunction of this enzyme and were compared to the rates of DNA synthesis in these tissues. Since DNA methylase levels from tumor nuclei were elevated compared to background, it is concluded that the undermethylation found in the tumor genomes of this system is not due to inactivation nor a significant deficiency of the activity of this enzyme relative to the demand in tumors for methylation of de novo synthesized DNA.
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PMID:DNA methylation and methylase levels in normal and malignant mouse hepatic tissues. 627 14

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

The E. coli dam (DNA adenine methylase) enzyme is known to methylate the sequence GATC. A general method for cloning sequence-specific DNA methylase genes was used to isolate the dam gene on a 1.14 kb fragment, inserted in the plasmid vector pBR322. Subsequent restriction mapping and subcloning experiments established a set of approximate boundaries of the gene. The nucleotide sequence of the dam gene was determined, and analysis of that sequence revealed a unique open reading frame which corresponded in length to that necessary to code for a protein the size of dam. Amino acid composition derived from this sequence corresponds closely to the amino acid composition of the purified dam protein. Enzymatic and DNA:DNA hybridization methods were used to investigate the possible presence of dam genes in a variety of prokaryotic organisms.
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PMID:The isolation and characterization of the Escherichia coli DNA adenine methylase (dam) gene. 630 Jul 69


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