Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previously, we isolated and characterized six Bacillus subtilis ada mutants that were hypersensitive to methylnitroso compounds and deficient in the adaptive response to alkylation. Cloning of the DNA complementing the defects revealed the presence of an ada operon consisting of two tandem and partially overlapping genes, adaA and adaB. The two genes encoded proteins with methylphosphotriester-DNA methyltransferase and O6-methylguanine-DNA methyltransferase activities, respectively. To locate the six mutations, the ada operon was divided into five overlapping regions of about 350 bp. The fragments of each region were amplified by polymerase chain reaction and analyzed by gel electrophoresis to detect single-strand conformation polymorphism. Nucleotide sequences of the fragments exhibiting mobility shifts were determined. Three of the mutants carried sequence alterations in the adaA gene: the adaA1 and adaA2 mutants had a one-base deletion and insertion, respectively, and the adaA5 mutant had a substitution of two consecutive bases causing changes of two amino acid residues next to the presumptive alkyl-accepting Cys-85 residue. Three mutants carried sequence alterations in the adaB gene: the adaB3 mutant contained a rearrangement, the adaB6 mutant contained a base substitution causing a change of the presumptive alkyl-accepting Cys-141 to Tyr, and the adaB4 mutant contained a base substitution changing Leu-167 to Pro. The adaB mutants produced ada transcripts upon treatment with low doses of alkylating agents, whereas the adaA mutant did not. We conclude that the AdaA protein functions as the transcriptional activator of this operon, while the AdaB protein specializes in repair of alkylated residues in DNA.
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PMID:Molecular analysis of Bacillus subtilis ada mutants deficient in the adaptive response to simple alkylating agents. 174 39

Many bacterial species have adaptive responses which protect against the toxicity and mutagenicity of methylating agents. Induced 3-methyladenine-DNA glycosylase and O6-methylguanine-DNA methyltransferase activities increase the cellular capacity of E. coli, B. subtilis, and M. luteus to repair toxic and mutagenic methylated base derivatives in DNA. The DNA methyltransferase or Ada protein of E. coli regulates the response and is converted into a strong transcriptional activator by self-methylation on repair of a methylphosphotriester in DNA. The multiple functions of the E. coli Ada protein (39 kDa) are split between two proteins, AdaA (24 kDa) and AdaB (20 kDa), in B. subtilis. Proteins (39 kDa) recognised by anti-Ada antibodies are efficiently induced in several enterobacterial species and correlate with increased DNA methyltransferase activities. In contrast, an "Ada-related" protein is only weakly induced in Salmonella typhimurium and no increase in DNA repair activity is detectable. The existence of adaptive responses in diverged bacterial species suggests the frequent occurrence of methylating agents in the environment. Several direct-acting methylating agents which are known to arise in the environment have been shown to induce the response. These include abundantly occurring methyl chloride, the antibiotic streptozotocin, the precursors of the known labile inducers N-methyl-N'-nitrosourea and N-methyl-N'-nitro-N-nitrosoguanidine and as shown in this paper, methyl radicals which may arise by the irradiation or oxidation of methyl compounds.
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PMID:Widespread adaptive response against environmental methylating agents in microorganisms. 194 38

By prophage transformation and subcloning, we have obtained Bacillus subtilis DNA fragments that could complement the hypersensitivity of ada (adaptive response deficient) mutants to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The nucleotide sequence contained two open reading frames that were assigned to the genes adaA and adaB, encoding methylphosphotriester-DNA methyltransferase and O6-methylguanine-DNA methyltransferase, respectively. These two genes overlap by 11 bp and comprise a small operon. The 1.6 Kb transcripts derived from the operon were detected in ada+ cells cultured in the presence of MNNG but not in control ada+ cells. From analysis of the syntheses of DNA alkyltransferases in the ada mutant cells harboring the plasmid carrying the complete or partial fragment, we conclude that the adaA gene product functions as a transcriptional activator of the ada operon, while the adaB gene product specializes in repair of mutagenic O6-methylguanine residues. Comparison with Escherichia coli ada operon showed that the two genes correspond to portions of the E. coli ada gene, implicating gene fusion or splitting as the origin of the difference in the organizations of the genes.
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PMID:Bacillus subtilis ada operon encodes two DNA alkyltransferases. 212 Jun 77

The multifunctional 39 kDa Escherichia coli Ada protein (O6-methylguanine-DNA methyltransferase) (EC 2.1.1.63), product of the ada gene, is a monomeric globular polypeptide with two distinct alkylacceptor activities located in two domains. The two domains are of nearly equal size and are connected by a hinge region. The Ada protein accepts stoichiometrically the alkyl group from O6-alkylguanine in DNA at the Cys-321 residue and from alkyl phosphotriester at the Cys-69 residue. This protein functions in DNA repair by direct dealkylation of mutagenic O6-alkylguanine. The protein methylated at Cys-69 becomes a transcriptional activator of the genes in the ada regulon, including its own. Each of the two domains functions independently as an alkyl acceptor. The purified homogeneous protein is unstable at 37 degrees C and spontaneously loses about 30% of its secondary structure in less than 30 min concomitant with a complete loss of activity. However, sedimentation equilibrium studies indicated that the inactive protein remains in the monomeric form without aggregation. Furthermore, electrospray mass spectroscopic analysis indicated the absence of oxidation of the inactive protein. This temperature-dependent inactivation of the Ada protein is inhibited by DNA. In the presence of increasing concentrations of urea or guanidine, the protein gradually loses more than 80% of its structure. The two alkyl acceptor activities appear to be differentially sensitive to unfolding and the phosphotriester methyltransferase activity is resistant to 7 M urea. The partial or complete unfolding induced by urea or guanidine is completely reversed within seconds by removal of the denaturant. The heat-coagulated protein can also be restored to full activity by cycling it through treatment with 8 M urea or 6 M guanidine. These results suggest that the nascent or unfolded Ada polypeptide folds to a metastable form which is active and that the thermodynamically stable structure is partially unfolded and inactive.
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PMID:Reversible folding of Ada protein (O6-methylguanine-DNA methyltransferase) of Escherichia coli. 948 44