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)

The Escherichia coli ada-alkB operon encodes a 39-kDa protein (Ada) that is a DNA-repair methyltransferase and a 27-kDa protein (AlkB) of unknown function. By DNA blot hybridization analysis we show that the alkylation-sensitive E. coli mutant BS23 [Sedgwick, B. & Lindahl, T. (1982) J. Mol. Biol. 154, 169-175] is a deletion mutant lacking the entire ada-alkB operon. Despite the absence of the ada gene and its product, the cells contain detectable levels of a DNA-repair methyltransferase activity. We conclude that the methyltransferase in BS23 cells is the product of a gene other than ada. A similar activity was detected in extracts of an ada-10::Tn10 insertion mutant of E. coli AB1157. This DNA methyltransferase has a molecular mass of about 19 kDa and transfers the methyl groups from O6-methylguanine and O4-methylthymine in DNA, but not those from methyl phosphotriester lesions. This enzyme was not induced by low doses of alkylating agent and is expressed at low levels in ada+ and a number of ada- E. coli strains.
...
PMID:A second DNA methyltransferase repair enzyme in Escherichia coli. 328 37

An Escherichia coli virus T1-induced DNA methyltransferase was identified by activity gel analysis in homogenates of infected E. coli DNA-adenine-methylation-deficient strains. Although the Mr of this protein (31,000) is in the same range as that of the E. coli DNA adenine methyltransferase, the two proteins are not closely related; the E. coli dam gene does not hybridize with T1 DNA. Selective conditions for measurement of the T1 activity were developed, and the enzyme was purified to functional homogeneity, as shown by activity analysis in polyacrylamide gels. Requirements for optimal activity of the viral enzyme were determined to be pH 6.9, ionic strengths below 0.1 M KCl, and a temperature between 40 and 43 degrees C. The Km for S-adenosyl-L-methionine is 4.9 microM. The purified T1 DNA methyltransferase is capable of methylating adenine in 5'-GATC-3' sites in vitro.
...
PMID:Identification, purification, and characterization of Escherichia coli virus T1 DNA methyltransferase. 331 2

A DNA methyltransferase of Mr = 140,000 that is active on both unmethylated and hemimethylated DNA substrates has been purified from the murine plasma-cytoma cell line MPC 11. The maximal rate of methylation was obtained with maintenance methylation of hemimethylated Micrococcus luteus or M13 DNAs. At low enzyme concentrations, the highest rate of de novo methylation occurred with single-stranded DNA or relatively short duplex DNA containing single-stranded regions. Strong substrate inhibition was observed with hemimethylated but not unmethylated DNA substrates. Fully methylated single-stranded M13 phage DNA inhibited neither the de novo nor the maintenance reactions, but unmethylated single-stranded M13 DNA strongly inhibited the maintenance reaction. The kinetics observed with hemimethylated and single-stranded substrates could be explained if the enzyme were to bind irreversibly to a DNA molecule and to aggregate if present in molar excess. Such aggregates would be required for activity upon hemimethylated but not single-stranded DNA. For de novo methylation of duplex DNA, single-stranded regions or large amounts of methyltransferase appear to be required. The relative substrate preference for the enzyme is hemimethylated DNA greater than fully or partially single-stranded DNA greater than fully duplex DNA.
...
PMID:De novo and maintenance DNA methylation by a mouse plasmacytoma cell DNA methyltransferase. 334 52

A DNA methyltransferase was isolated from a eucaryotic, Chlorella-like green alga infected with the virus PBCV-1. The enzyme recognized the sequence GATC and methylated deoxyadenosine solely in GATC sequences. Host DNA, which contains GATC sequences, but not PBCV-1 DNA, which contains GmATC sequences, was a good substrate for the enzyme in vitro. The DNA methyltransferase activity was first detected about 1 h after viral infection; PBCV-1 DNA synthesis and host DNA degradation also began at about this time. The appearance of the DNA methyltransferase activity required de novo protein synthesis, and the enzyme was probably virus encoded. Methylation of DNAs with the PBCV-1-induced methyltransferase conferred resistance of the DNAs to a PBCV-1-induced restriction endonuclease enzyme described previously (Y. Xia, D. E. Burbank, L. Uher, D. Rabussay, and J. L. Van Etten, Mol. Cell. Biol. 6:1430-1439). We propose that the PBCV-1-induced methyltransferase protects viral DNA from the PBCV-1-induced restriction endonuclease and is part of a virus-induced restriction and modification system in PBCV-1-infected Chlorella cells.
...
PMID:DNA methyltransferase induced by PBCV-1 virus infection of a Chlorella-like green alga. 353 3

In extracts of E. coli treated with an adapting regime of MNNG, the induced 39kd Ada protein having O6-MeG-DNA methyltransferase activity is processed to a 19kd active domain corresponding to the C-terminal half of the intact protein. This proteolytic processing has been followed on Western immunoblots using antisera raised against the 19kd fragment. Initial processing at 25 degrees C or 37 degrees C mainly generates a fragment of mol. wt. 24kd which then undergoes a slower second cleavage to generate the 19kd active domain. Preceding this second cleavage site is a sequence of amino acids Thr- -Gly-Met-Thr- -Lys that also occurs at another site in the N-terminal half of the 39kd methyltransferase. It is proposed that this sequence is a recognition site for proteolytic activity. On the basis of cleavage of the Ada protein at either one or both of these sites, fragments may be generated of mol. wt. 24kd and 19kd containing the active site for O6-methylguanine and O4-methylthymine repair, and 15kd and 20kd, containing the active site for methylphosphotriester repair. These observations explain previous reports by others on the existence in cell extracts of multiple methyltransferase activities of different sizes recognizing O-methyl lesions in DNA. The cellular protease involved is resistant to a wide range of protease inhibitors.
...
PMID:Proteolytic processing of the Ada protein that repairs DNA O6-methylguanine residues in E. coli. 354 5

Mer- human cells, which lack O6-methylguanine DNA methyltransferase activity, are extremely sensitive to alkylation induced killing, mutation and sister chromatid exchange. We have analyzed a Mer+, a Mer-, and a Mer- revertant HeLa cell line and found that the methyltransferase deficiency correlates with increased levels of mutation and sister chromatid exchange, but does not correlate with increased killing of Mer- HeLa cells by alkylating agents. Furthermore, we show that HeLa Mer- cells repair N-3-methylguanine and N-3-methyladenine just as efficiently as HeLa Mer+ cells.
...
PMID:DNA alkylation repair and the induction of cell death and sister chromatid exchange in human cells. 380 5

The ada+ gene product, a DNA methyltransferase present in extracts from an Escherichia coli strain constitutive for the adaptive response, removes only half of the methyl phosphotriesters from alkylated DNA. Since DNA phosphotriesters occur in two isomeric configurations (denoted Rp and Sp), we examined whether this reflects a stereospecific mode of repair by the methyltransferase. Analysis by reverse-phase HPLC, phosphorus NMR and circular dichroism established that only triesters in the Sp configuration are acted upon by the E. coli extract.
...
PMID:Stereospecific removal of methyl phosphotriesters from DNA by an Escherichia coli ada+ extract. 390 61

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 Burkitt's lymphoma cell line Raji has a Mex+ phenotype. It is more resistant to killing by alkylating agents than a sub line (Raji TK-) which is Mex-. A reduction in O6-methylguanine (O6MeG)-DNA methyltransferase can be brought about by growing Raji cells in the presence of free O6MeG. The depletion in enzyme activity is specific and reversible; removal of O6MeG from the medium results in the restoration of methyltransferase activity within 4 h. Raji cells, in which methyltransferase has been reduced by this treatment to below detectable levels, are not sensitised to killing by N-methyl-N'-nitro-N-nitrosoguanidine or the cross-linking nitrosoureas, 1,3-bis(2-chloroethyl)-1-nitrosourea and 1-(2-chloroethyl)-1-nitrosourea. This implies that adducts at the O6 atom of guanine in DNA are not potentially cytotoxic lesions. Secondly, it suggests that a defect other than the lack of methyltransferase is responsible for the sensitivity of Mex- cells to killing by alkylating agents.
...
PMID:The cytotoxic and mutagenic effects of alkylating agents on human lymphoid cells are caused by different DNA lesions. 400 64

We have developed a facile procedure for the purification of DNA methyltransferase activity from human placenta. The procedure avoids the isolation of nuclei and the dialysis and chromatography of large volumes. A purification of 38,000-fold from the whole cell extract has been achieved. The procedure employs ion exchange, affinity, and hydrophobic interaction chromatography coupled with preparative glycerol gradient centrifugation. A protein of 126,000 daltons was found to copurify with the activity and was the major band seen in the most highly purified material after SDS gel electrophoresis. This observation, coupled with an observed sedimentation coefficient of 6.3S, suggests that the enzyme is composed of a single polypeptide chain of this molecular weight. Hemimethylated DNA was found to be the preferred substrate for the enzyme at each stage in the purification. The ratio of the activity of the purified product on hemimethylated to that on unmethylated M13 duplex DNA was about 12 to 1. Thus, the purified activity has the properties postulated for a maintenance methyltransferase. The availability of highly purified human DNA methyltransferase should facilitate many studies on the structure, function, and expression of these activities in both normal and transformed cells.
...
PMID:Purification of human DNA (cytosine-5-)-methyltransferase. 408 9


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

---