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

---

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

Histones (from calf thymus or from human placenta), if renatured in the presence of EDTA, caused a severe inhibition of in vitro methylation of double-stranded DNA (from Micrococcus luteus) by human placenta DNA methyltransferase. The absence of EDTA during the histone renaturation procedure abolished--at least in the 'physiological' range of the histones/DNA ratio--the inhibition. The H1 component was responsible for this inhibition, no effect being exerted by the other histones. H1 preparations were more effective if renatured in the presence of EDTA--90% inhibition being reached at a 0.3:1 (w/w) H1/DNA ratio. It seems likely that the requirement for the presence of EDTA during the renaturation process is correlated to its ability to induce a fairly stable ordered conformation of the histones, although this effect could also be shown with the 'inactive' H2a, H2b and H3 components, and was instead less evident with histone H1. The restriction to histone H1 of the ability to inhibit enzymic DNA methylation may account for the lower methylation levels present in the internucleosomal DNA of mammalian chromatin.
...
PMID:Histones and DNA methylation in mammalian chromatin. Differential inhibition by histone H1. 188 42

Incubation of 5-azacytosine-substituted DNA ([5-aza-C]DNA) with nuclear proteins leads to the formation of highly stable DNA . protein complexes which remain intact in the presence of 1 M NaCl and/or 0.6% Sarkosyl. The proteins involved in binding double-stranded [5-aza-C]DNA in these stable complexes comprise a specific subset of non-histone nuclear proteins that includes DNA methyltransferase. Complex formation does not require S-adenosylmethionine and does not involve covalent linkage of protein to DNA or modification of 5-azacytosine residues. Non-histone nuclear proteins do not form complexes with double-stranded unsubstituted DNA that are resistant to dissociation with NaCl and Sarkosyl but are capable of forming such complexes with single-stranded DNA regardless of whether it contains 5-azacytosine residues or not. However, it can be demonstrated 1) that single-stranded regions do not account for stable binding of proteins to native [5-aza-C]DNA and 2) that many nuclear proteins which form stable complexes with single-stranded DNA are incapable of forming such complexes with double-stranded [5-aza-C]DNA. Synthesis of [5-aza-C]DNA by cells growing in the presence of either 5-azacytidine or 5-aza-2'-deoxycytidine leads to rapid loss of extractable DNA methyltransferase (Creusot, F., Acs, G., and Christman, J.K. (1982) J. Biol. Chem. 257, 2041-2048). Analogous depletion of non-histone nuclear proteins capable of forming stable complexes with [5-aza-C]DNA in vitro is observed, suggesting that the same proteins can form highly stable complexes with [5-aza-C]DNA in vitro and in vivo. Formation of stable complexes between non-histone nuclear proteins and [5-aza-C]DNA could potentially affect not only the activity of DNA methyltransferase but the action of other regulatory proteins or enzymes that interact with DNA. Such interactions could explain effects of 5-azacytidine on gene expression that cannot be directly linked to loss of methyl groups from DNA.
...
PMID:Formation of highly stable complexes between 5-azacytosine-substituted DNA and specific non-histone nuclear proteins. Implications for 5-azacytidine-mediated effects on DNA methylation and gene expression. 257 44

O6-Methylguanine-DNA methyltransferase, a DNA repair enzyme which transfers the methyl group of O6-methylguanine residue to a cysteinyl residue in the methyltransferase itself, was examined in rat organs by quantifying the S-methylcysteine formed in the methyl acceptor protein. Among the various organs examined, the spleen exhibited the highest enzyme specific activity followed by the thymus, liver, lung and testis. Brain had the lowest activity. The patterns of subcellular distribution of the methyltransferase in spleen and liver were different: while 75-80% of the activity was present in the nuclear fraction of the spleen, 54% of the activity in the liver was found in the nuclei and 35% in the cytosolic fraction. Forty-five and thirty-five percent of the total nuclear enzyme activity could be extracted with 1 M and 2 M NaCl solutions, respectively, indicating that the repair enzyme is not tightly bound to the nuclear matrix. When isolated nuclei were incubated with [methyl-3H]DNA substrate and subsequently fractionated into histone and non-histone protein fractions, over 90% of the radioactivity was coeluted on a Bio-Rex 70 column with the non-histone fraction and only a negligible amount of radioactivity was found to be associated with the histone fraction. The molecular mass of the [methyl-3H]methyltransferase in the non-histone fraction was determined to be 23,000, and its pI value was found to be 6.6 by two-dimensional polyacrylamide gel electrophoresis.
...
PMID:Studies on the distribution of O6-methylguanine-DNA methyltransferase in rat. 394 77

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

The E2a region of the Ad2 genome encodes the Ad2-specific DBP. An inverse correlation between the level of DNA methylation at the 5'-CC*GG-3' sites of the E2a region and the extent of expression of DBP has been demonstrated in Ad2-transformed hamster cell lines (Vardimon et al. 1980). Four different leaders are used in the transcription of the E2a region in cells productively infected with Ad2. The leader located at coordinate 75 on the viral genome is used early after infection and the other three leaders are used late after infection (Chow et al. 1979). The analysis of the integration patterns of the viral DNA in the Ad2-transformed cell lines has revealed that the early leader is deleted in the cell lines which do not express the DBP (Vardimon and Doerfler 1981). The late leader located at coordinate 72 on the viral genome is present. The region encoding that late leader has been subcloned, and the cytoplasmic RNA from the cell line which expresses the DBP has been analyzed. It has been shown that the late leader is used in transformed cells. Hence the absence of the early leader cannot be the immediate reason for the lack of expression of the DBP. Correlations between DNA methylation and the absence of gene expression may indicate that methylation regulates gene expression or that methylation is the consequence of lacking gene expression. In order to decide between these alternatives an in vitro system has been employed. The HindIII A fragment of the Ad2 DNA which encodes the DBP has been methylated in vitro by the HpaII DNA methyltransferase. Methylated or unmethylated HindIII A fragment has been microinjected into the nuclei of Xenopus laevis oocytes. Unmethylated HindIII A fragment has been found to be expressed as specific viral RNA, whereas no viral RNA can be found in oocytes microinjected with methylated HindIII A fragment. The possibility of a nonspecific inhibitory factor in the methylated DNA preparation has been ruled out by the simultaneous microinjection of sea urchin histone gene DNA together with the methylated HindIII A fragment. Histone genes are expressed, while the expression of the methylated viral gene is blocked. By using the single-strand-specific endonuclease S1 we have shown that in Xenopus laevis oocytes initiation of transcription of the E2a region starts exactly at the same site as in Ad2 productively infected cells. These results provide direct evidence for the notion that DNA methylation at specific sites is involved in the regulation of gene expression.
...
PMID:Can DNA methylation regulate gene expression? 630 51

In many viral and nonviral eukaryotic systems, an inverse correlation has been observed between the extent of DNA methylation at 5'-C-C-G-G-3' sites and the extent of expression of specific genes as mRNA. The E2a region of adenovirus serotype 2 (Ad2) DNA encodes the Ad2-specific DNA binding protein required for viral DNA replication. In three lines of Ad2 transformed hamster cells (HE1, HE2, and HE3), multiple copies of the major part of the Ad2 genome persist in an integrated state. Cell lines HE2 and HE3 do not express the DNA-binding protein whereas line HE1 does so. It has been shown that, in cell line HE1, all 5'-C-C-G-G-3' (Hpa II/MspI) sites in the E2a region remain unmethylated. Conversely, in lines HE2 and HE3 lacking expression of the E2a region all Hpa II sites are methylated. The cloned E2a region of Ad2 DNA, the HindIII A fragment in pBR322, was methylated in vitro by using Hpa II DNA methyltransferase (5'-C-C*G-G-3') or was left unmethylated. In vitro methylation did not break or nick supercoiled circular DNA. Methylated or unmethylated DNA was then microinjected into the nuclei of Xenopus laevis oocytes, and the subsequent synthesis of Ad2-specific RNA was monitored. In vitro-methylated DNA remained in the methylated state for 24 hr on microinjection into nuclei of xenopus oocytes; unmethylated DNA remained unmethylated. When the injected DNA had been methylated by using Hpa H DNA methyltransferase, Ad2-specific RNA was not synthesized as late as 24 hr after microinjection. Unmethylated DNA was readily expressed into Ad2-specific RNA. As an internal control, unmethylated histone genes (h22 DNA) from sea urchin were microinjected together with methylated E2a DNA from Ad2. Ad2-specific RNA was not found; h22 DNA-specific RNA was readily detected. This finding ruled out nonspecific inhibitory effects in the methylated DNA preparation. Ir was also shown that transcription of the unmethylated HindIII A fragment of Ad2 DNA in Xenopus oocytes was initiated on the late promoter of the E2a region. The same promoter was used in productively infected KB cells. Methylation by BsuRI methylse (5'-G'G-C*C-3') did not inactivate the HindIII A fragment. These results provide evidence for the notion that methylated sequences at highly specific sites are involved in the regulation of gene expression. The actual nature of the regulatory signal is not yet understood.
...
PMID:Expression of a cloned adenovirus gene is inhibited by in vitro methylation. 695 Nov 63

Treating activated CD4+ T cells with DNA methyltransferase inhibitors modifies gene expression and induces autoreactivity. Adoptive transfer of viable polyclonal autoreactive cells causes a lupus-like disease, most likely because of one or more effector functions expressed by the autoreactive cells. However, the number of potential effector mechanisms expressed by polyclonal cells is large. To more readily identify responsible mechanisms, we asked if autoimmunity can be induced by using the conalbumin-reactive, cloned Th2 cell line D10.G4.1, treated with 5-azacytidine (5-azaC) or procainamide (Pca). Treated, but not untreated, cells responded to syngeneic APCs without Ag, overexpressed LFA-1, spontaneously lysed syngeneic macrophages, and secreted relatively large amounts of IL-6, small amounts of IL-4, and no detectable IL-2 nor IFN-gamma. Adoptive transfer of treated, but not untreated, cells induced a severe immune complex glomerulonephritis, pulmonary alveolitis, central nervous system abnormalities including fibrinoid necrosis, karyorrhexis, and meningitis, and bile duct proliferation with periportal inflammatory cell infiltration resembling primary biliary cirrhosis. Anti-ssDNA, anti-dsDNA, and anti-histone Abs were also found. These experiments demonstrate that modification of this cloned T cell line with DNA methyltransferase inhibitors is sufficient to cause an autoimmune disease, with features of lupus as well as autoimmune liver disease. The results also raise the possibility that macrophage lysis, IL-6 secretion, and LFA-1 overexpression could contribute to the disease process. This system may be useful in testing the role of these and other pathologic mechanisms in the development of specific autoimmune lesions.
...
PMID:Mechanism of drug-induced lupus. I. Cloned Th2 cells modified with DNA methylation inhibitors in vitro cause autoimmunity in vivo. 753 91

The inhibitory effect that H1 histone exerts on the in vitro DNA methylation process, catalysed by mammalian DNA methyltransferase, together with the relative hypomethylation of linker DNA in eukaryotic cells chromatin, suggest that this hypomethylated state of linker DNA can be of importance in allowing or regulating H1-dependent chromatin condensation. In native oligonucleosomes (olnu), i.e., in chromatin fragments consisting of 5-20 nucleosomes each, there was a correlation between the effects of H1 on the DNA ellipticity at 280 nm and the in vitro assayed methyl-accepting ability. The same was true in H1-depleted or in H1-reconstituted preparations. Artificial methylation caused olnu DNA to lose its ability to allow cooperative H1-H1 interactions under ionic strength conditions similar to those known to affect the transition of the 10-nm filament to the 30-nm chromatin fiber. These results suggest that hypomethylation of linker DNA plays a role in the H1-H1 interactions that are needed for solenoid condensation.
...
PMID:Does hypomethylation of linker DNA play a role in chromatin condensation. 760

A specific mechanism was given for ethionine-induced alpha-fetoprotein gene activity and is as follows: 1. Ethionine acts on competent cell types (e.g. stem cells) having one alpha-fetoprotein-enhancer-albumin gene region that is active and possesses embryonic-like low levels of S-adenosyl-L-methionine synthesis: DNA methylase genes for the enhancer regions are in the heterochromatic state. 2. ATP: L-methionine-S-adenosyltransferase acts upon ethionine and ATP to form S-adenosyl-L-ethionine; this lowers the amount of S-adenosyl-L-methionine synthesized and in turn also the synthesis of methyl-nicotinamide; the concentration of nicotinamide increases; there is an inhibition of polyADP ribosylation; hyporibosylation of histone 1 of nucleosomes; deblocking of embryonic type heterochromatin; and finally the second alpha-fetoprotein gene becomes activated. 3. Reversal occurs with the introduction of methionine; increase of S-adenosyl-L-methionine synthesis; increased methylnicotinamide synthesis; increased polyADP-ribose synthesis; ribosylation of H-1 protein to normal levels; and then the packing configuration of chromatin causes rerepression of alpha-fetoprotein genes. It is suggested that ethionine has the ability to perturb a methyl-sensitive heterochromatin that is peculiar to chromatin synthesized during embryogenesis. Therefore such repressed embryonic genes as alpha-fetoprotein are differentially susceptible to low concentrations of active methyl groups. Ethionine causes this hypomethylated heterochromatin by interference with S-adenosyl-L-methionine synthesis.
...
PMID:A specific mechanism for ethionine-induced embryonic gene activity. 768 49

Escherichia coli Dam DNA methyltransferase can methylate genomic GATC sites when expressed in Saccharomyces cerevisiae. Others have observed changes in the level of methylation at specific sites and suggested that these changes are related to transcriptional state or chromosomal context. To test directly the influence of nucleosome location on the ability of Dam methyltransferase to modify GATC sites in chromatin, we analyzed minichromosomes containing precisely positioned nucleosomes in dam-expressing yeast strains. Levels of methylation at individual GATC sites were rigorously quantified by an oligonucleotide-probing procedure. Within the linker and adjacent 21 bp of nucleosome-associated DNA, GATC sites were highly methylated, whereas methylation was severely inhibited by histone-DNA contacts nearer to the nucleosomal pseudodyad. Other DNA-protein complexes also interfere with Dam methylation. These data are consistent with a model in which nucleosomes exert a repressive influence on the biological functions of DNA by restricting access of trans-acting factors to DNA.
...
PMID:Positioned nucleosomes inhibit Dam methylation in vivo. 810 16


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

---