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)

In Shigella sonnei cells there is a host DNA specificity system responsible for modification and restriction of DDII phage. DNA methylase from Shigella stutzeri cells is specific for adenine and catalyses the appearance of 6-'-methylaminopurine in the acceptory DNA. Methylases from Shigella sonnei cells are specific for adenine and cytosine and provide for the presence of 6'-methylaminopurine and 5'-methylcytosine in DNA. The modifying activity of these cells may be equally likely associated with both the enzymes. A simplified version of the additional methylation test has been developed for the study of enzyme specificity. The results of additional and cross methylation suggest that several adenine methylases are present in the cells of these Shigella, one of these enzymes being shared by Shigella stutzeri and Shigella sonnei. The DNA's isolated from Shigella sonnei and Shigella stutzeri cells are undermethylated and in vitro undergo additional methylation upon incubation with the appropriate enzyme.
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PMID:[System of host specificity and the DNA methylases of shigellae and their phages]. 37 52

An improved method of purification of DNA methylase from Krebs II ascites cells is reported. The enzyme sediments at 8.3 S on glycerol-gradients and a major band on SDS polyacrylamide gel electrophoresis has a molecular weight of 184 000. Aggregation occurs at low salt and this may interfere with enzymic activity. The preferred double stranded DNA substrate is that rendered partially unmethylated by an in vitro repair mechanism or by isolation from methionine starved cells. Methylation of native partially methylated DNA is favoured under conditions of low salt and high temperature; conditions which encourage 'breathing' of the DNA. Methylation of native, unmethylated DNA also involves breathing but results in formation of a salt resistant tight binding complex between the enzyme and the DNA.
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PMID:Mouse DNA methylase: methylation of native DNA. 42 61

The possibility that carcinogens may affect methylase-mediated methylation of replicating DNA was investigated. A system eminently suitable for this purpose is liver regenerating after partial hepatectomy, as one injection of dimethylnitrosamine (DMN) given during the ensuing period of increased DNA synthesis induces hepatocellular carcinoma. Methylation of DNA by DNA methylase normally occurs only in proportion to DNA synthesis. Therefore simultaneous measurements were made of synthesis (incorporation of [14C]adenine into DNA adenine, or of d[5-3H]cytidine into DNA cytosine), and of methylation (incorporation of [methyl-3H]methionine into 5-methylcytosine of DNA) in liver regenerating after partial hepatectomy. After treatment with DMN, the ratio of methylation: synthesis remained within the normal range. Methyl methanesulphonate (MMS), a compound which damages DNA in regenerating liver in a similar but not identical way to DMN and which does not induce tumors in liver even when given after partial hepatectomy, caused an increase in methylation in relation to synthesis. These experiments therefore do not support the view that altered DNA methylase activity is involved in carcinogenesis.
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PMID:Effect of a single treatment with the alkylating carcinogens dimethylnitrosamine and methyl methanesulphonate on liver regenerating after partial hepatectomy. IV. Effect on methylase-mediated methylation of DNA. 47 54

After a 10 min- or more prolonged incubation of transformed mouse fibroblasts (L.-cells) with [3H]-thymidine or [3H-methyl]-methionine and a subsequent centrifugation of cell lysates in an alkaline sucrose gradient the DNA radioactivity is detected in long (28, 33 and 45S) and short (5, 13 and 18S) fragments. An increase in cell concentration in the cultural layer results in inhibition of 5S fragments linkage rather than in inhibition of their synthesis. The blocking of the Okazaki fragment linkage may be regarded as one of the inhibitory molecular mechanisms of cell depletion. Both in the case of normal and suppressed (by 99%) replication by arabofuranosylcytosine [3H]-thymidine and [3H-5-methyl] cytosine are detected in the Okazaki fragments (5S) as well as in some discrete lower molecular weight fractions (lesser than 5S) of newly synthesized DNA. Thus, replicative methylation of DNA in the fibroblasts occurs in the replicative fork during DNA synthesis and the functioning DNA methylase is an indispensable component of the replicative complex. The methylation of Okazaki fragments is non-chaotic and has a specificity other than that of total DNA. This may be due to the multiplicity and different specificity of nuclear DNA-methylases. Thus, there exist in animal cells replicative and post-replicative methylation of DNA, which may differ in the nature of substrates and enzymes, in specificity of recognizable sequences and in their functional significanse.
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PMID:[Methylation of newly synthesized DNA in mouse fibroblast culture]. 49 87

DNA methylase has been purified 660-fold from nuclei from regenerating rat liver. The enzyme is able to methylate single stranded (ss) and double stranded (ds) DNA, the only reaction product being 5-methylcytosine. Previously unmethylated double stranded DNA from prokaryotes (M.luteus) as well as from eukaryotes (Ascaris suis) can serve as substrates. The synthetic copolymers (dG-dC)n . (dC-dG)n and (dG,dC)n are also methylated. While SV40 DNA is almost not methylated, PM2 DNA is a good substrate even in the supercoiled form. The enzyme methylates 1 in 17 bases in heterologous M.luteus DNA, but only 1 in 590 in homologous rat liver DNA. The high methylation level of M.luteus DNA, an analysis of the methylated pyrimidine isostichs and a preliminary dinucleotide analysis suggest that all the CpGs in a DNA can be methylated.
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PMID:DNA-methylase from regenerating rat liver: purification and characterisation. 67 48

E. coli DNA methylase has been used to methylate chromatin DNA in vitro. At saturation only 50% of the chromatin DNA becomes methylated. The methylated regions of chromatin correspond to that fraction of the chromatin which is sensitive to staphylococcal nuclease. Using in vitro methylated chromatin followed by nuclease digestion movement of chromatin proteins along the DNA can be detected. By this criterion, sonication of chromatin or precipitation with MnCl2 causes 10% of the previously uncovered methylated regions to become covered by protein. Reconstitution of methylated chromatin results in the randomization of the chromatin proteins. Using nuclei which were methylated in vitro we have demonstrated that a small degree of protein sliding does occur during the preparation of chromatin from nuclei. Finally, we have prepared open region DNA by polylysine titration. This procedure does not cause displacement of chromatin proteins.
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PMID:Methylation of chromatin DNA. 78 84

DNA-methylase activities which methylate cytosine residues in homo- and heterologous DNA were detected in mitochondria and nuclei from rat liver and beef heart. Adenine modifying DNA-methylases in mitochondria and nuclei were not found. DNA from mitochondria and nuclei differ significantly in the methylation degree and in the pattern of the 5-methyl-cytosine distribution by pyrimidine isostichs as DNA in vivo and in vitro being methylated. Mitochondrial DNA methylase has the maximum activity at 30 degrees and pH 7.8 this enzyme(s) differ(s) from the nuclear one(s) in the pH dependence of its activity. After exhaustive in vitro methylation of various DNA by the nuclear enzyme DNA-methylase from mitochondria additionally introduces CH3 groups from S-adenosylmethionine into these DNA (about 3 times more CH3 groups than nuclear enzyme). Nuclear DNA-methylase also methylates DNA which is previously fully-methylated by the mitochondrial enzyme, but to a lesser degree. In conditions of exhaustive DNA methylation mitochondrial enzyme introduces into E. coli B DNA about four times more methyl groups as compared to the nuclear one. After the methylation of E. coli B DNA by mitochondrial enzyme the label (3H-methyl) was detected predominantly in mono-, and in case of nuclear enzyme--in di- and tripyrimidine fragments. Mitochondrial DNA-methylase differs from the nuclear one in the nature of recognized DNA sequences; these enzymes seems to be represented by different proteins. The mitochondrial enzyme methylates shorter nucleotide sequences in DNA as compared to the nuclear DNA-methylase. All these data suggest there exist organoid specificity of genome methylation in animal cell and the modification-restriction systems in animal nucleus and mitochondria are different in character.
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PMID:[DNA-methylase activities from animal mitochondria and nuclei: different specificity of DNA methylation]. 102 67

The nucleotide composition, relative concentration of pyrimidine clusters, and the degree of methylation of the mitochondrial and nuclear DNA's of various vertebrates and the protozoan Crithidia oncopelti have been studied. With respect to the relative concentration of GC pairs, the mtDNA of animals (bull, rat) does not differ from the corresponding nDNA. The relative concentration of GC pairs in the mtDNA of certain fish and birds is 1.5-2.5 mole% higher than in the respective nDNA. The kinetoplast DNA of the protozoan C. oncopelti (where the relative concentration of the GC pairs is 42.9 mole %) differs very sharply in composition from the nDNA (where the relative concentration of GC pairs is 51.3 mole %). The mtDNA's and kDNA's studied are distinguished from the respective nDNA'S by a lower degree of clustering of pyrimidine nucleotides. The proportion of mono- and dipyrimidine fragments in the mtDNA and kDNA is 30 mole %, while in the nDNA it does not exceed 23 mole %. The relative concentration of long pyrimidine clusters (hexapyrimidine clusters of larger) in the mtDNA is smaller than in the nDNA by a factor of 2-5. The low degree of clustering of the pyrimidine nucleotides is apparently characteristic of all the known mtDNA's and may support the fact that they have a single type of organization and are of a single origin. All the vertebrate mtDNA's studied contain 5-methylcytosine as a minor base (1.5-3.15 mole %), and their level of methylation is 1.5-2 times greater than that in the respective nDNA's. It has been shown that animals display species specificity with respect to the 5-methylcytosine content in the mtDNA. Its distribution among the pyrimidine clusters in the bovine heart mtDNA differs substantially from that in the nDNA. This suggests that the methylation specificities of nuclear and mitochondrial DNA are different. A DNA methylase, which effects the in vitro methylation of cytosine residues both in the homologous mtDNA and in different heterologous DNA's, has been found in rat liver and bovine heart mitochondria. The specificity of the in vitro methylation of the cytosine residues in the same heterologous Escherichia coli B DNA by the nuclear and mitochondrial enzymes is different: The mitochondrial enzyme methylates predominantly in monopyrimidine fragments, and the nuclear enzyme methylates mostly in di- and tripyrimidine fragments. They, therefore, recognize different nucleotide sequences.
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PMID:Structure of animal mitochondrial DNA: nucleotide composition, pyrimidine clusters, and methylation character. 102 50

On growing the cells of Bacillus brevis S methionine-auxotroph mutant in the presence of [Me-3H]methionine, practically all the radioactivity incorporated into DNA is found to exist in 5-methylcytosine and N6-methyladenine. The analysis of pyrimidine isopliths isolated from DNA shows that radioactivity only exists in mono- and dinucleotides and the content of 5-methylcytosine in R-m5 C-R and R-m5 C-T-R oligonucleotides is equal. The analysis of dinucleotides isolated from DNA by means of pancreatic DNAase hydrolysis allows the nature of purine residues neighbouring 5-methylcytosine to be identified and shows that 5-methylcytosine localizes in G-m5 C-A and G-m5 C-Tr fragments. B. brevis S DNA methylase modifying cytosine residues recognizes the GCA/TGC degenerate nucleotide sequence which is a part of the following complementary structure with a two-fold rotational axis of symmetry: (5')...N'-G-C-T-G-C-N... (3') (3')...N-C-G-A-C-G-N'... (5') (Methylated cytosine residues are askerisked). Cytosine-modifying DNA methylase activity is isolated from B. brevis cells; it is capable of methylating in vitro homologous and heterologous DNA. Hence DNA in bacterial cells can be undermethylated. This enzyme methylates cytosine residues in native and denatured DNA in the same nucleotide sequences. Specificity of methylation of cytosine residues in vitro and in vivo does not depend on the nature of substrate DNA. DNA methylases of different variants of B. brevis (R, S, P+, P-)) methylate cytosine residues in the same nucleotide sequences. It means that specificity or methylation of DNA cytosine residues in the cells of different variants of B. brevis is the same.
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PMID:On the nature of the cytosine-methylated sequence in DNA of Bacillus brevis var. G.-B. 118 Sep 70

A DNA methylase has been purified 270-fold from HeLa cell nuclei by chromatography on DEAE-cellulose, phosphocellulose, and hydroxyapatite. The enzyme transfers methyl groups from S-adenosyl-L-methionine to cytosine residues in DNA. The sole product of the reaction has been identified as 5-methylcytosine. The enzyme is able to methylate homologous (HeLa) DNA, although to a lesser extent than heterologous DNA. This may be due to incomplete methylation of HeLa DNA synthesized in vivo. The HeLa enzyme can methylate single-stranded DNA, and does so to an extent three times greater than that of the corresponding double-stranded DNA. In single-stranded M. luteus DNA, at least 2.4% of the cytosine residues can be methylated in vitro by the enzyme. The enzyme also can methylate poly (dG-dC-dG-dC) and poly (dG, dC). Bilateral nearest neighbors to the 5-methylcytosine have been determined with M. luteus DNA in vitro and HeLa DNA in vivo. The 5' neighbor can be either G or C while the 3' neighbor is always G and this sequence is, thus, p(G/C)pmCpG.
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PMID:DNA methylase from HeLa cell nuclei. 118 40


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