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 (Δ 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 Δ ssrS strain in the presence of high concentrations of H 2 O 2 . 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 Δ ssrS strain. Finally, we performed comparative proteomic analyses of the wild-type and Δ ssrS strains, confirming that Δ ssrS bacteria have reduced levels of the proteins AhpC and Tpx involved in H 2 O 2 reduction. Our findings substantiate the crucial role of the riboregulator 6S RNA for bacterial coping with extreme stresses.