Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.1.1.37 (DNA methyltransferase)
 4,983 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of 3-alkyl substituted imidazotetrazinones on methylation of DNA has been studied in drug sensitive and resistant cell lines. The 3-methyl analogue (Temozolomide) has been shown to cause a decrease in the level of 5-methylcytosine in newly synthesized DNA in both cell lines, although the effect occurred at lower drug concentrations in the drug sensitive cell line. In order to investigate the mechanism of hypomethylation of DNA, calf thymus DNA was alkylated in vitro by both Temozolomide and the 3-ethyl analogue, CCRG 82019, and the alkylated DNA was shown to inhibit the transfer of methyl groups from S-adenosyl-L-methionine to M. lysodeikticus DNA by purified eukaryotic DNA methylase. Neither free drug alone or unmodified DNA affected the methylase reaction. Calf thymus DNA modified with CCRG 82019 was more effective as a methylase inhibitor than DNA modified with Temozolomide, which was a reverse of the order of potencies of the free drugs against tumour cells in culture. CCRG 82019 modified DNA also formed a more stable complex with nuclear proteins. Alterations in the level of 5-methylcytosine in DNA may be important in the alteration of gene expression by these agents.
 ...
PMID:Antitumour imidazotetrazines and gene expression. 320 8

Acrolein, a reactive metabolite of cyclophosphamide, may be responsible for bladder cancer induced by cyclophosphamide. DNA methylase was isolated from the liver and urothelium of rats by high salt extraction of purified nuclei. Acrolein at 10 microM inhibited liver and bladder DNA methylase activity by 30-50%. Kinetic studies with the liver enzyme showed a competitive type of inhibition with a Ki of 6.7 microM. Both dithiothreitol and glutathione afforded protection to the enzyme when added to the assay. At near equimolar concentrations of glutathione to acrolein, the methylase retained 80-90% activity. An increase in DNA had no effect on the inhibition by acrolein, whereas increased amounts of protein protected against acrolein inhibition, suggesting that acrolein reacted with the DNA methylase protein. On the other hand, DNA that had been reacted with acrolein was unable to serve as a substrate for DNA methylase. As the DNA adducts increased the methylation of the DNA decreased. Thus, acrolein has the ability to react with DNA and the DNA methylase protein, either of which results in inhibition of DNA methylation.
 ...
PMID:Inhibition of DNA methylase activity by acrolein. 334 85

In order to detect possible m5C photoproducts, highly purified rat liver DNA-cytosine methyltransferase was used to specifically generate m5C with a radioactive methyl group. When these DNAs were subjected to a large dose (10 kJ/m2) of 254 nm or 302 nm ultraviolet light (UVB) to enhance the yield, two labeled photoproducts were detected and isolated by reverse phase HPLC after formic acid hydrolysis. Further studies using acetone as a triplet state sensitizer and UVB irradiation suggested that photoproduct II was activated via a triplet state while the more polar photoproduct I was not. Photoreversion of the purified photoproducts with 10 kJ/m2 254 nm light demonstrated the following reactions: Photoproduct I regenerated m5C, while photoproduct II is split and regenerated m5C and photoproduct I. These results suggest that photoproduct I is monomeric while photoproduct II dimeric, and from the latter's elution position possibly a cyclobutyl type dimer arising from a reaction with an adjacent cytosine. Using d[TTG] and d[Cm5CG] as models of typical sequences, irradiation with 10 kJ/m2 254 nm or 302 nm, respectively, gave rise to a small component having altered mobility in sequencing gels. The altered mobility trinucleotides were resistant to degradation by PI and micrococcal nucleases as expected from photodimerization of the pyrimidine bases. Furthermore, oligonucleotide substrates containing m5C were synthesized and shown to be susceptible to T4 endonuclease v action at locations consistent with d[Cm5C] photodimer formation when irradiated in the UVB range.
 ...
PMID:UV-induced photoproducts of 5-methylcytosine in a DNA sequence context. 337 57

Sodium selenite is a good inducer of hemoglobin production in Friend erythroleukemic cells (FELC). At a concentration of 20 microM 70-80% of the cells produce hemoglobin and the DNA is hypomethylated. What is the mechanism for sodium selenite alteration of the DNA methylation pattern? Experiments with methionine adenosyltransferase (the enzyme that synthesizes adenosylmethionine) showed little effect of selenite on the activity of this enzyme in vitro or in vivo. Therefore, FELC are able to synthesize S-adenosylmethionine in the presence of sodium selenite. When sodium selenite was added to an in vitro assay for DNA methylase, the enzyme was non-competitively inhibited by 80% at 20 microM selenite with a Ki of 6 microM. DNA methylase isolated from control and selenite-treated FELC was purified through a DEAE-Sephacel column and no difference in activity was found. In the presence of selenite, DNA methylase is very sensitive to selenite inhibition, but removal of the selenite restores activity. However, DNA synthesized by FELC grown in the presence of selenite (no DNA methylase activity) was found to be hypomethylated. These results suggest that DNA methylase activity is inhibited in FELC grown in the presence of sodium selenite.
 ...
PMID:A study of the mechanism of selenite-induced hypomethylated DNA and differentiation of Friend erythroleukemic cells. 346 78

5'-Deoxy-5'-(methylthio)adenosine (MTA) alone and in combination with methionine was found to increase frequencies of background HGPRT mutation and SCE in V79 Chinese hamster cells. The same agents exert a comutagenic action on these effects as well as upon mutation induction in Escherichia coli stain AB1157 (but not in its non-adaptable derivative ada-6) following treatment with N-methyl-N-nitrosourea (MNU). MTA plus methionine also enhanced the lethal action of MNU on hamster cells. The effects observed may tentatively be ascribed to hypomethylation due to inhibition of DNA methylase by MTA.
 ...
PMID:Mutagenic and comutagenic action of 5'-deoxy-5'-(methylthio)adenosine. 351 30

The origin and function of the large amount of 5-methylcytosine in plant DNA is not well understood. As a tool for in vitro studies of methylcytosine formation in plants we have isolated and characterized the DNA methyltransferase present in germinating wheat embryo. An enzyme fraction enriched 300-fold over the tissue homogenate was obtained by salt extraction of nuclei, chromatography on DEAE-cellulose, Sephadex G-75, blue Sepharose and on DNA immobilized on cellulose. It catalyzes the methylation of cytosine residues in double-stranded DNAs isolated from wheat, maize, calf thymus or bacteria using S-adenosylmethionine as methyl donor. The efficient methylation of both an unmethylated plasmid DNA and its hemimethylated derivative indicate that the wheat DNA methylase can function de novo and in maintenance methylation. A relative molecular mass of 50,000-55,000 was estimated by gel permeation chromatography and sucrose density gradient centrifugation. Polyacrylamide gel electrophoresis showed the presence of a protein of Mr = 50,000 and one other component (Mr = 35,000). The preference for endogenous, double-stranded DNA as substrate and the lower molecular mass distinguish wheat DNA methyltransferase from the DNA methylases obtained from mammalian sources. The properties of the wheat enzyme resemble, however, those of the DNA methylase isolated from the alga Chlamydomonas reinhardii, suggesting that plant cells possess their own type of DNA methyltransferase for the biosynthesis of their high methylcytosine content in DNA.
 ...
PMID:DNA methylation in wheat. Purification and properties of DNA methyltransferase. 362 12

We have purified the DNA methylase from mouse ascites tumour cells to a specific activity of 11,500 units per mg protein using denatured Micrococcus luteus DNA as methyl acceptor. Methyl groups are transferred to cytosines almost exclusively in CpG dinucleotides. The purified enzyme contains two polypeptides of molecular mass 185 and 160 kDa, and an antiserum raised in a rabbit to the purified enzyme specifically reacts with these two proteins in crude extracts. The two proteins can be partially separated by affinity chromatography when activity is associated with the 185 kDa protein which can be proteolytically degraded to give polypeptides of 170 and later 100 and 50 kDa. Only the 185 kDa methylase is lost when cells are treated with azadeoxycytidine and this is the predominant form firmly bound in the nucleus of dividing cells. Antibody bound to the 185 kDa band in protein blots will itself bind native DNA methylase, which can be detected by its binding 14C-labelled, azacytosine-containing DNA.
 ...
PMID:Mouse ascites DNA methylase: characterisation of size, proteolytic breakdown and nucleotide recognition. 375 72

In vivo and in vitro evidence is presented implicating a function of GATC methylation in the Escherichia coli replication origin, oriC, during initiation of DNA synthesis. Transformation frequencies of oriC plasmids into E. coli dam mutants, deficient in the GATC-specific DNA methylase, are greatly reduced compared with parental dam+ cells, particularly for plasmids that must use oriC for initiation. Mutations that suppress the mismatch repair deficiency of dam mutants do not increase these low transformation frequencies, implicating a new function for the Dam methylase. oriC DNA isolated from dam- cells functions 2- to 4-fold less well in the oriC-specific in vitro initiation system when compared with oriC DNA from dam+ cells. This decreased template activity is restored 2- to 3-fold if the DNA from dam- cells is first methylated with purified Dam methylase. Bacterial origin plasmids or M13-oriC chimeric phage DNA, isolated from either base substitution or insertion dam mutants of E. coli, exhibit some sensitivity to digestion by DpnI, a restriction endonuclease specific for methylated GATC sites, showing that these dam mutants retain some Dam methylation activity. Sites of preferred cleavage are found within the oriC region, as well as in the ColE1-type origin.
 ...
PMID:Importance of state of methylation of oriC GATC sites in initiation of DNA replication in Escherichia coli. 389 29

The activity of de novo DNA (cytosine-5-)-methyltransferase (DNA methylase) in various rat tissues after administration of a single dose of N-methyl-N-nitrosourea (MNU) has been analyzed. The total and specific activities of the DNA methylase of the brain, where tumor induction is important, are increased. In kidney, the DNA methylase activity first increases up to 16 h and decreases afterwards. Liver DNA methylase activity does not change. This organ is not susceptible to MNU induced cancers. Because organs in which the DNA methylase activity is high or increased after MNU are more prone to carcinogenesis by this compound, we argue that there is a relationship between the effects of MNU and DNA methylase activity.
 ...
PMID:Changes in de novo DNA (cytosine-5-)-methyltransferase activity in oncogenically susceptible rat target tissues induced by N-methyl-N-nitrosourea. 394 88

The endogenous DNA methylase in nuclei isolated from growing mouse cells preferentially methylates DNA in micrococcal nuclease-resistant regions probably as a result of the location in these regions of the preponderance of hemimethylated sites. Added mouse ascites cell DNA methylase catalyses the methylation of exposed, nuclease-sensitive DNA in chromatin from growing or non-growing mouse or insect cells. The poor acceptor ability of nuclease-resistant regions in this situation is due to the presence of histone proteins which block de novo methylation. Transcriptionally active regions of chromatin are selectively methylated in vitro by either endogenous or added DNA methylase.
 ...
PMID:Methylation of chromatin in vitro. 396 9


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