Overexpression of an antisense RNA, ArrS, increases the acid resistance of Escherichia coli

The antisense RNA ArrS is complementary to a sequence in the 5' untranslated region of the gadE T3 mRNA, the largest transcript of gadE, which encodes a transcriptional activator of the glutamate-dependent acid resistance system in Escherichia coli. Expression of arrS is strongly induced during the stationary growth phase, particularly under acidic conditions, and transcription is dependent on σ(S) and GadE. The aim of the present study was to clarify the role of ArrS in controlling gadE expression by overexpressing arrS in E. coli. The results showed a marked increase in the survival of arrS-overexpressing cells at 2 h after a shift to pH 2.5. This was accompanied by increased expression of gadA, gadBC and gadE. The level of gadE T3 mRNA decreased markedly in response to arrS overexpression, and was accompanied by a marked increase in gadE mRNA T2. T2 mRNA had a monophosphorylated 5' terminus, which is usually found in cleaved mRNAs, and no T2 mRNA was observed in an RNase III-deficient cell strain. In addition, T2 mRNA was not generated by a P3-deleted gadE-luc translational fusion. These results suggest strongly that T2 mRNA is generated via the processing of T3 mRNA. Moreover, the T2 mRNA, which was abundant in arrS-overexpressing cells, was more stable than T3 mRNA in non-overexpressing cells. These results suggest that overexpression of ArrS positively regulates gadE expression in a post-transcriptional manner.