The induction of Escherichia coli aidB gene in Salmonella typhimurium

Background and Purpose: In Escherichia coli, the main response specific for alkylation damage has been called the adaptive response. It is a set of genes composed of the ada, alkA, alkB, and aidB genes. The AidB protein is involved in a detoxilication pathway for N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), although its function is still unclear Adaptive response is not detectable in the closely related Salmonella typhimurium. It has been suggested that the lack of this response is due to the low ability of methylated Ada(ST) to act as a transcriptional activator. We analyzed the induction of E. coli aidB gene in S. typhimurium applying aidB-lacZ operon fusion. The activation of aidB promoter was monitored in ada-dependent conditions as well as ada-independent induction during oxygen-limiting or acidic conditions. Material and Methods: The induction of E. coli aidB gene was monitored by assaying P-galactosidase activity in extract obtained from cells containing operon fusion of Mu d1 (bla, lac) to aidB. Results: Methylating agents MMNG and methyl methanesulfonate (MMS) induced ada-dependent transciption of aidB gene in S. typhimurium at the same level as in E. coli. Alkylating agents N-methyl-N-nitrosourea (MNU) and ethyl methanesulfonate (EMS) did not induce significant expression of aidB gene, Decreasing extracellular pH as well as semianaerobiosis, ada-independent induction, increased aidB gene expression in S. typhimurium. Conclusions: MNNG and MMS induction of E. coli aidB gene in S. typhimurium through ada-dependent mode indicates the possibility that methylated Ada(ST) acts as a transcriptional activator.