Involvement of the nemRA operon of escherichia coli in glyoxal resistance

Abstract

Glyoxal(GO) is an aldehyde compound that is toxic and mutagenic. Glyoxal-resistant mutants were isolated from Escherichia coli MG1655 strain lacking yqhD gene, encoding an aldehyde reductase for glyoxal, on LB plates containing 5-10 mM glyoxal. By isolating nearby TnphoA-132 insertions the glyoxal-resistant mutants, the mutaion sites were mapped and analysed. One of them was NemA over-expressing strain, which has a single nucleotide change in NemR-binding seqeunce upstream of nemRA operon. N-ethylmaleimide reductase encoded by NemA is a enzyme that reduces N-ethylmaleimide. nemA and nemR constitute an operon, in which NemR serves as a negative regulator for its transcription. A mutaion in NemR- binding site is expected to prevent binding of NemR, overproducing both NemR and NemA. GloA encoding glyoxalase I for catalyzing methyl-glyoxal (MG) is located downstream of the nemRA operon, whose transcription was increased in NemR-binding site mutation. Thus, it is proposed that over-expressing of both NemA and GloA is required for GO resistance confered by the NemR-binding site mutation.