Disease relevance of alkA

• Expression of the ada and alkA genes, both of which are involved in the adaptive response of Escherichia coli to alkylating agents, is positively controlled by Ada protein, the product of the ada gene [1].
• The results show a clear relationship between the levels of N3-methyladenine and toxicity in an alkA/tag glycosylase mutant that cannot remove the adduct from its genome [2].
• Bacillus subtilis alkA gene encoding inducible 3-methyladenine DNA glycosylase is adjacent to the ada operon [3].

High impact information on alkA

• The cloned ada and alkA genes and purified Ada protein have been used in cell-free systems to identify the inducing signal [4].
• The derived APDG protein sequence of 253 amino acids and the 3-meAde-DNA glycosylase II of E. coli coded for by the alkA gene have regions of conserved sequences [5].
• We described previously the isolation of a Saccharomyces cerevisiae 3-methyladenine (3-MeAde) DNA glycosylase repair gene (MAG) by its expression in glycosylase-deficient Escherichia coli alkA tag mutant cells and its ability to rescue these cells from the toxic effects of alkylating agents [6].
• Here we extend this cross-species functional complementation approach to the isolation of a full-length human 3-MeAde DNA glycosylase cDNA that rescues alkA tag E. coli from killing by methyl methanesulfonate, and we have mapped the gene to human chromosome 16 [6].
• A region of the Ada DNA-repair protein required for the activation of ada transcription is not necessary for activation of alkA [7].

Chemical compound and disease context of alkA

• Cloning and characterization of the alkA gene of Escherichia coli that encodes 3-methyladenine DNA glycosylase II [8].
• Single crystals of 3-methyladenine-DNA glycosylase II produced from the alkA gene of Escherichia coli have been obtained by the method of vapour diffusion with polyethylene glycol 6000 as precipitant at pH 8 [9].
• Our data show that MNNG induction of UVM is independent of ada, alkA and alkB genes and define UVM as an inducible mutagenic phenomenon distinct from the E. coli adaptive and SOS responses [10].
• Moreover, while ada and alkA E. coli mutants showed increased sensitivity to streptozotocin, they were not more sensitive to the other alkylating agents evaluated [11].

Biological context of alkA

• We constructed hybrid plasmids carrying an alkA'-lacZ' fusion, with the proper control region for alkA expression [12].
• Nucleotide sequence of a DNA fragment containing the alkA gene and its control region has been determined using a chemical method [12].
• The alkA gene of Escherichia coli encodes a DNA glycosylase involved in base excision repair of DNA alkylation damage [13].
• Since both 5-formyluracil and 5-hydroxymethyluracil are major products formed in DNA by exposure to ionizing radiation, these results implicate the alkA gene function also in the repair of oxidative DNA damage [13].
• The actions of mutant Ada proteins on the ada and alkA promoters in vivo were investigated using an artificially composed gene expression system [14].

Associations of alkA 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 [1].
• These results indicate that the alkA gene codes for 3-methyladenine DNA glycosylase II [8].
• When cells harboring the alkA+ plasmids were grown in the presence of low doses of a simple alkylating agent (adapted condition), the activity of 3-methyladenine DNA glycosylase II was increased [8].
• Ada is converted into an efficient transcriptional activator by transferring a methyl group from a DNA methylphosphotriester to its own Cys-69 residue and then binds to a DNA sequence (the Ada box) present in both the ada and alkA promoters [7].
• While 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea induces alkA, other nitrosoureas, mechlorethamine, and cis-DDP do not cause expression of this gene [15].

Regulatory relationships of alkA

• These results suggest that the mechanism by which Ada activates ada transcription differs from that by which it activates alkA transcription [7].

Other interactions of alkA

• Furthermore, the sensitivity and the spontaneous mutation rate observed in the double mutant alkA- uvrA- are almost identical to those of the uvrA- mutant [16].
• Thus, both aidA and aidB share with adaptive response a common regulatory mechanism involving the ada gene [17].
• Cells deleted for the polA (DNA polymerase I) or priA (primosome) genes are as sensitive to MMS and MNNG as alkA tag bacteria [18].

Analytical, diagnostic and therapeutic context of alkA

• 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 [14].

References