Disease relevance of ada

• The ada gene of Escherichia coli K12, the regulatory gene for the adaptive response of bacteria to alkylating agents, was cloned and placed under the control of the lac regulatory region on a multicopy runaway plasmid, thereby yielding a hybrid plasmid pYN3059 [1].
• An amino-terminal sequence and total amino acid composition of the purified Ada protein were in accord with nucleotide sequence of the ada gene, determined by the dideoxy method using M13 phage [1].
• Bacillus subtilis alkA gene encoding inducible 3-methyladenine DNA glycosylase is adjacent to the ada operon [2].
• Lines infected with each of the four retroviruses were selected for neo expression and found to have intact proviral integration and ada gene expression [3].
• The transfectant cells expressed the truncated E. coli MT were resistant to alkylating agents as same as the transfectant cells with the intact ada gene in cell killing, sister-chromatid exchange induction and host-cell reactivation of adenovirus 5 [4].

High impact information on ada

• The cloned ada and alkA genes and purified Ada protein have been used in cell-free systems to identify the inducing signal [5].
• A methylation-dependent electrostatic switch controls DNA repair and transcriptional activation by E. coli ada [6].
• An alkylation repair deficient mutant of Escherichia coli (tag ada), lacking DNA glycosylase activity for removal of alkylated bases, was transformed by a genomic yeast DNA library and clones selected which survived plating on medium containing the alkylating agent methylmethane sulphonate [7].
• The ada promoter has a stretch of seven adenosine residues (A7) in its upstream region [8].
• We have determined the kinetics of initiation of transcription of the wild-type ada promoter by abortive initiation assays [8].

Chemical compound and disease context of ada

• Alteration of lysine 178 in the hinge region of the Escherichia coli ada protein interferes with activation of ada, but not alkA, transcription [9].
• Mammalian O6-alkylguanine-DNA alkyltransferases (AGTs) are readily inactivated by incubation with the pseudosubstrate, O6-benzylguanine, but the equivalent protein from the Escherichia coli ogt gene is much less sensitive and the Saccharomyces cerevisiae and E. coli ada gene product AGTs are completely resistant to this compound [10].
• Specific cysteine residues at possible methyl acceptor sites of the Ada protein of Escherichia coli were converted to other amino acids by site-directed mutagenesis of the cloned ada gene of E. coli [11].
• Escherichia coli has two O6-methylguanine DNA methyltransferases that repair alkylation damage in DNA and are encoded by the ada and ogt genes [12].
• Cadmium and mercury ions inhibited the promotion of ada and alkA gene expression in the adaptive process induced by methylating agents such as N-methyl-N-nitrosourea (MNU), methyl methanesulfonate (MMS) and methyl iodide in Escherichia coli [13].

Biological context of ada

• Induction and autoregulation of ada, a positively acting element regulating the response of Escherichia coli K-12 to methylating agents [14].
• These results support the reported in vitro substrate specificities for both ogt and ada ATases [15].
• Cell extracts from several independently derived ada mutants contain variable amounts of an altered 37-kd protein after an inducing alkylation treatment [16].
• We obtained evidence that the ada and alkB genes constitute an operon [17].
• Transcriptional activation of ada does not occur if both the amino- and carboxyl-terminal domains are produced separately within the same cell [9].

Anatomical context of ada

• Plasmids containing an N-terminal fragment of the ada+ gene which encoded only one of the two methyltransferase activities of the Ada protein did not significantly protect E. coli or CHO cells against MNNG [18].
• However, NIH-3T3 cells expressing ada were only slightly more resistant to BCNU than controls, possibly because most of the ada protein was cytoplasmic rather than nuclear as suggested by immunohistochemical stain [3].
• O6-alkylguanine-DNA-alkyltransferase (ATase)-deficient murine haemopoietic stem cells were transfected, following electroporation, with a G418-selectable expression vector containing the protein coding region of the Escherichia coli ATase gene ada [19].
• After recombination with a Chinese hamster metallothionein I gene promoter, the ada gene was microinjected into C3H/HeN mouse zygotes [20].

Associations of ada with chemical compounds

• However, responses of the two transcription reactions to methylating agents differed; ada transcription was stimulated by methylnitrosourea, while alkA transcription was suppressed [21].
• Genes belonging to the adaptive response are positively regulated by the ada gene; the Ada protein acts as a transcriptional activator when methylated in one of its cysteine residues at position 69 [22].
• We constructed hybrid plasmids carrying an alkB'-lacZ' fusion, with or without the ada control region, and investigated expression of the alkB gene in response to the alkylating agent [17].
• Transfer of a methyl group to Cys-69 by repair of a methylphosphotriester lesion converts Ada into a transcriptional activator of the ada and alkA genes [9].
• AdaK178P (lysine 178 changed to proline) is completely defective for the transcriptional activation function of ada while it is completely proficient for transcriptional activation of alkA [9].

Regulatory relationships of ada

• Deletion of the carboxyl-terminal 67 amino acids of Ada abolished the ability of the unmethylated form of the protein to inhibit activation of ada transcription but not the ability of the methylated form to activate ada or alkA transcription [23].
• Although ogt was expressed at slightly higher levels than the truncated ada in the transfected cells, this could not account for the differential protection observed [24].
• Expression of the Escherichia coli aidB gene is induced in vivo by alkylation damage in an ada-dependent pathway and by anaerobiosis or by acetate at pH 6.5 in an ada-independent fashion [25].

Other interactions of ada

• Common features in the Ada-binding regions of ada and aidB are a high A/T content, the presence of an inverted repeat structure, and their position relative to the transcriptional start site [22].
• Furthermore, an increase in the level of the Ada protein, caused by the runaway plasmid pYN3059 in which the ada gene is regulated by the lac promoter, inhibited UV-mediated recA gene expression even in cells to which the MNNG-adaptive treatment had not been applied [26].
• A recA-ada hybrid gene inducible by DNA damage [27].

Analytical, diagnostic and therapeutic context of ada

• We have shown by genetic mapping, molecular cloning, and DNA sequencing that four Escherichia coli mutants, which express the adaptive response to alkylation damage constitutively, are mutated in the ada gene [28].
• When the ada gene with the Ala69 mutation was introduced into the cell, there was little induction of expression of either the ada or the alkA genes, even after treatment with an alkylating agent, in agreement with the data obtained from studies in vitro [11].
• RNA transcripts of the chimeric ada gene were identified in the livers of these transgenic mice using dot and Northern blot analyses [20].

References