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)

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

The human melanoma cell line M21 can be induced to differentiate into oligodendrocyte-like cells with concommitant cessation of cell division. Cytosine-arabinoside, 5-aza-2'-deoxycytidine, hydroxyurea, aphidicolin, and phorbol-12-myristate-13-acetate were found to be potent differentiation inducers. We have analyzed the changes of methylation of DNA cytosines that occur after treatment of M21 cells with these compounds. Although DNA methylation levels remain unchanged in the presence of aphidicolin and phorbol ester, 5-aza-2'-deoxycytidine-induced differentiation of these cells results in a 40% DNA demethylation. On the other hand, hydroxyurea and cytosine-arabinoside treatment causes DNA hypermethylation, which, in the case of the cytidine analogue is of only transient nature. These results show that the differentiation of human melanoma cells can be accompanied by variable changes of DNA methylation levels. In another set of experiments, the DNA methylation levels have been analyzed during cytosine-arabinoside-induced differentiation of human K562 erythroleukemia cells. In this system, a transient DNA demethylation precedes the establishment of the differentiated phenotype. Since DNA replication is inhibited, this demethylation cannot be explained by inhibition of the maintenance activity of DNA methyltransferase, but is more likely caused by an active excision of 5-methylcytosine from DNA.
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PMID:The DNA methylation system in proliferating and differentiated cells. 247 29

Cytosine methylation within DNA has been implicated in genetic imprinting, X-chromosome inactivation, regulation of tissue-specific gene expression, aging, and cancer. Unfortunately, DNA (cytosine-5)-methyltransferases (EC 2.1.1.37) from various mammalian sources have been difficult to isolate and stabilize, precluding investigations of these critical enzymes. We describe a novel FPLC purification of the 190,000 Mr DNA methyltransferase from mouse Friend erythroleukemia cells. The homogeneous 190 kD Mr form of the enzyme is the only polypeptide detected at various stages of cell growth and has not undergone detectable N-terminal proteolysis.
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PMID:Purification and stabilization of mouse DNA methyltransferase. 786 41

Cytosine methylation is an important mechanism of gene regulation in mammals. Mouse embryos with reduced DNA methylation due to targeted disruption of the DNA methyltransferase gene show deregulated expression of imprinted genes. Loss of imprinting associated with loss of allele-specific methylation is one example of an epigenetic alteration found in tumor cells. Changes in DNA methylation may also be associated with facilitating protooncogene expression and inactivating tumor suppressor genes. However, cytosine methylation has additional deleterious consequences for the genome as well. CpG dinucleotides, the target of DNA methylation, are five-fold underpresented in the genome due to the high mutability of methylated cytosine. C-T transition mutations resulting from deamination of 5-methylcytosine are involved in both genetic disease and cancer. Lastly, aberrant DNA methylation may promote the genetic instability of a chromosomal locus. We review the genetic and epigenetic roles for DNA methylation during tumorigenesis gleaned from altered methycytosine patterns in tumor cells, and from pharmacologic, dietary or genetic manipulation of DNA methylation levels.
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PMID:Experimental manipulation of genomic methylation. 911 Apr 3

Cytosine (C-5)-specific DNA methyltransferases share a set of ten conserved motifs distributed evenly throughout the entire polypeptide chain. The first conserved motif contains a Phe, which is intimately associated with cofactor recognition. In the pseudo-DNA methyltransferase M.SpoI, encoded by the pmt1 gene in Schizosaccharomyces pombe, a Tyr replaces this Phe residue. We describe the properties of a mutant form of M.MspI, a typical cytosine (C-5)-specific DNA methyltransferase, in which Tyr replaces the conserved Phe. This mutant shows differences in ternary complex formation and in the pattern of covalent complex formation with an inhibitory, fluorinated DNA duplex which may be due to anomalous hydrogen bonding between the mutant Tyr hydroxyl group and the catalytic loop of the enzyme or through interference with cofactor binding.
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PMID:Substitution of the conserved phenylalanine in the S-adenosyl-L-methionine binding site of M.MspI with tyrosine modifies the kinetic properties of the enzyme. 962 62

The recessive autosomal disorder known as ICF syndrome (for immunodeficiency, centromere instability and facial anomalies; Mendelian Inheritance in Man number 242860) is characterized by variable reductions in serum immunoglobulin levels which cause most ICF patients to succumb to infectious diseases before adulthood. Mild facial anomalies include hypertelorism, low-set ears, epicanthal folds and macroglossia. The cytogenetic abnormalities in lymphocytes are exuberant: juxtacentromeric heterochromatin is greatly elongated and thread-like in metaphase chromosomes, which is associated with the formation of complex multiradiate chromosomes. The same juxtacentromeric regions are subject to persistent interphase self-associations and are extruded into nuclear blebs or micronuclei. Abnormalities are largely confined to tracts of classical satellites 2 and 3 at juxtacentromeric regions of chromosomes 1, 9 and 16. Classical satellite DNA is normally heavily methylated at cytosine residues, but in ICF syndrome it is almost completely unmethylated in all tissues. ICF syndrome is the only genetic disorder known to involve constitutive abnormalities of genomic methylation patterns. Here we show that five unrelated ICF patients have mutations in both alleles of the gene that encodes DNA methyltransferase 3B (refs 5, 6). Cytosine methylation is essential for the organization and stabilization of a specific type of heterochromatin, and this methylation appears to be carried out by an enzyme specialized for the purpose.
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PMID:Chromosome instability and immunodeficiency syndrome caused by mutations in a DNA methyltransferase gene. 1064 11

Cytosine methylation levels and susceptibility to drug-induced hypomethylation have been studied in several Nicotiana tabacum (tobacco) DNA repetitive sequences. It has been shown using HapII, MspI, BamHI and Sau3AI methylation-sensitive restriction enzymes that the degree of 5'-mCmCG-3' methylation varied significantly between different repeats. There were almost saturation levels of 5-methylcytosine at the inner (3') cytosine position and variable degrees of methylation at the outer (5') cytosine at the enzyme recognition sites. The non-transcribed high copy satellite sequences (HRS60, GRS) displayed significant heterogeneity in methylation of their basic units while middle repetitive sequences (R8.1, GRD5, 5S rDNA) were more uniformly modified at both cytosine residues. Dihydroxypropyladenine (DHPA) treatment, which is thought to reduce DNA methyltransferase activity by increasing S-adenosylhomocysteine levels, resulted in extensive demethylation of the outer cytosine in all repeats, and the partial hypomethylation of cytosines at the inner positions in less densely methylated repeats such as HRS60 and GRS. The results suggest that hypomethylation of 5'-mCmCG-3' sites with DHPA is a gradual non-random process proceeding in the direction mCmCG-->CmCG-->CCG. The 18S-5.8S-25S rDNA was remarkably hypomethylated relative to the 5S rDNA at all restriction sites studied. Fluorescence in-situ hybridization showed that DNA decondensation within and between the 18S-5.8S-25S and 5S rDNA loci was variable in different nuclei. All nuclei had condensed and decondensed sequence. The chromatin of 18S-5.8S-25S rDNA was more readily digested with micrococcal nuclease than the 5S rDNA suggesting that the overall levels of decondensation were higher for 18S-5.8S-25S rDNA. Variable decondensation patterns within and between loci were also observed for GRS and HRS60. Cytosine methylation of the tobacco repeats is discussed with respect to transcription, overall levels of condensation and overall structure.
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PMID:Comparative analysis of DNA methylation in tobacco heterochromatic sequences. 1103 22

Cytosine methylation of mammalian DNA is essential for the proper epigenetic regulation of gene expression and maintenance of genomic integrity. To define the mechanism through which demethylated cells die, and to establish a paradigm for identifying genes regulated by DNA methylation, we have generated mice with a conditional allele for the maintenance DNA methyltransferase gene Dnmt1. Cre-mediated deletion of Dnmt1 causes demethylation of cultured fibroblasts and a uniform p53-dependent cell death. Mutational inactivation of Trp53 partially rescues the demethylated fibroblasts for up to five population doublings in culture. Oligonucleotide microarray analysis showed that up to 10% of genes are aberrantly expressed in demethylated fibroblasts. Our results demonstrate that loss of Dnmt1 causes cell-type-specific changes in gene expression that impinge on several pathways, including expression of imprinted genes, cell-cycle control, growth factor/receptor signal transduction and mobilization of retroelements.
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PMID:Loss of genomic methylation causes p53-dependent apoptosis and epigenetic deregulation. 1113 87

The DNA methylase inhibitors, 5-azacytidine and 5-aza-2'-deoxycytidine inhibited adventitious shoot induction in Petunia leaf cultures. Cytosine methylation status at CCGG sites in shoot- and callus-inducing culture treatments was analysed by coupled restriction enzyme digestion (HpaII or MspI) and random amplification. Two differentially methylated genomic DNA bands from the PCR products were cloned (OPU9-1 and OPU9-2) and sequenced. The open reading frames contained in OPU9-1 and OPU9-2 showed similarity to CDC48 and MADS-box genes, respectively. Cytosine methylation was restored at CCGG sites when the leaf explants were transferred from medium containing the drugs to medium without the drugs, simultaneously recovering the ability to develop adventitious shoot buds. Furthermore, combined bisulphite treatment and restriction analysis revealed differential methylation of CGCG sites in the drug-treated and control cultures. These results demonstrate that cytosine methylation at CCGG and CGCG sites within a MADS-box gene and a CDC48 homologue, among others, shows strong positive correlation with adventitious shoot bud induction in Petunia leaf explants.
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PMID:Cytosine methylation occurs in a CDC48 homologue and a MADS-box gene during adventitious shoot induction in Petunia leaf explants. 1270 82

Cytosine methylation is common, but not ubiquitous, in eukaryotes. Mammals and the fungus Neurospora crassa have about 2-3% of cytosines methylated. In mammals, methylation is almost exclusively in the under-represented CpG dinucleotides, and most CpGs are methylated whereas in Neurospora, methylation is not preferentially in CpG dinucleotides and the bulk of the genome is unmethylated. DNA methylation is essential in mammals but is dispensable in Neurospora, making this simple eukaryote a favoured organism in which to study methylation. Recent studies indicate that DNA methylation in Neurospora depends on one DNA methyltransferase, DIM-2 (ref. 6), directed by a histone H3 methyltransferase, DIM-5 (ref. 7), but little is known about its cellular and evolutionary functions. As only four methylated sequences have been reported previously in N. crassa, we used methyl-binding-domain agarose chromatography to isolate the methylated component of the genome. DNA sequence analysis shows that the methylated component of the genome consists almost exclusively of relics of transposons that were subject to repeat-induced point mutation--a genome defence system that mutates duplicated sequences.
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PMID:The methylated component of the Neurospora crassa genome. 1271 82


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