Involvement of E. coli 6S RNA in Oxidative Stress Response

6S RNA, a small non-coding RNA present in almost all bacteria, inhibits transcription via direct binding to RNA polymerase holoenzymes. The mechanism of 6S RNA action was investigated to a large extent in E. coli, however, lack of 6S RNA (Delta ssrS) was demonstrated to be unfavorable but not essential for cell survival under various growth conditions. In the present study, we revealed, for the first time, a lethal phenotype of the Delta ssrS strain in the presence of high concentrations of H2O2. This phenotype was rescued by complementation of the ssrS gene on a plasmid. We performed comparative qRT-PCR analyses on an enlarged set of mRNAs of genes associated with the oxidative stress response, allowing us to identify four genes known to be involved in this pathway (soxS, ahpC, sodA and tpx) that had decreased mRNA levels in the Delta ssrS strain. Finally, we performed comparative proteomic analyses of the wild-type and Delta ssrS strains, confirming that Delta ssrS bacteria have reduced levels of the proteins AhpC and Tpx involved in H2O2 reduction. Our findings substantiate the crucial role of the riboregulator 6S RNA for bacterial coping with extreme stresses.