# Involvement of _E. coli_ 6S RNA in Oxidative Stress Response
## 3 Discussion  
NcRNAs are widely activated in response to different stresses and/or adaptation to unfavorable conditions, where they regulate the expression of single or multiple targets. For example, DsrA, ArcZ, and RprA ncRNAs are known to activate translation of RpoS (\(\sigma^{38}\)), the sigma factor specific for stationary phase transcription and stress response [9]. Other small ncRNAs, such as OxyS and RyhB have dozens of mRNA targets, representing genes that are essential for coping with oxidative conditions or iron starvation, respectively [49]. According to transcriptomic data, _E. coli_ 6S RNA regulates the expression of hundreds of genes, also including several stress response proteins, translation and transcription factors as well as enzymes involved in various metabolic processes [17; 22]. However, such a global influence impedes attempts to identify the most affected targets, for example in analyses of 6S RNA knockout strains where direct and indirect dysregulation effects at multiple levels contribute to the observed physiological state. A first key step in this endeavor is the identification of specific phenotypes of 6S RNA-deficient cells to obtain decisive evidence for certain pathways being affected by this ncRNA. Here, we discovered a lethal phenotype of _E. coli_ \(\Delta ssrS\) bacteria when exposed to elevated concentrations of H\({}_{2}\)O\({}_{2}\) (10 to 20 mM). Through complementation using a plasmid-borne \(ssrS\) gene we were able to fully rescue the lethal phenotype, thus proving that \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Gene** & **Name** & **Function** & **References** \\ \hline \multicolumn{4}{c}{Major regulators of oxidative stress response} \\ \hline _oxyR_ & H\({}_{2}\)O\({}_{2}\)-inducible genes activator & activator of H\({}_{2}\)O\({}_{2}\)-inducible genes (including _lstG_, _alpyC_, _oxyS_) & [36; 37] \\ _oxyS_ & non-coding RNA OxyS & regulates expression of a number of genes by interaction with mRNAs via antisense mechanism & [38] \\ _soxS_ & regulatory protein SoxS & RNAP-binding protein, activator of superoxide response & [37] \\ _crp_ & cAMP-activated global transcriptional regulator & activates transcription by RNAP recruitment & [39] \\ \hline \multicolumn{4}{c}{Proteins involved in degradation of H\({}_{2}\)O\({}_{2}\) and/or other ROS *} \\ \hline _katG_ & catalase-peroxidase & degradation of H\({}_{2}\)O\({}_{2}\) & [37] \\ _katE_ & catalase HPII & degradation of H\({}_{2}\)O\({}_{2}\) & [37] \\ _vujA_ & cytochrome peroxidase Ccp & degradation of H\({}_{2}\)O\({}_{2}\) & [40] \\ _ttuE_ & thioredoxin/glutathione peroxidase BtuE & non-specific peroxidase, degradation of H\({}_{2}\)O\({}_{2}\) & [41] \\ _atpC_ & alkyl hydroperode reductase subunit C & degradation of H\({}_{2}\)O\({}_{2}\) and organic hydroperoxides & [37] \\ _tpx_ & thiol peroxidase & degradation of H\({}_{2}\)O\({}_{2}\) and organic hydroperoxides & [42] \\ _sodA_ & superoxide dismutase [Mn] & degradation of superoxide anion radicals & [43] \\ _osmC_ & peroxideoxin OsmC & degradation of organic hydroperoxides & [44] \\ \hline \multicolumn{4}{c}{General stress proteins} \\ \hline _rpoS_ & RNA polymerase sigma factor RpoS & stationary phase and general stress response gene activation & [45] \\ _yanA_ & peroxide stress resistance protein YaaA & protects DNA from oxidative damage & [46] \\ _uspE_ & universal stress protein E & general response to different environmental stresses including anti-oxidative function, essential for cellular adhesion, agglutination, & [47] \\ _uspF_ & universal stress protein UP12 & cell motility and swimming & [48] \\ \hline \multicolumn{4}{c}{Control proteins} \\ \hline _rpoD_ & RNA polymerase sigma factor RpoD, \(\sigma^{20}\) & primary sigma factor during exponential growth & \\ _syrA_ & DNA gyrase subunit A & type II topoisomerase, DNA supercoiling & \\ _gunD_ & guanine deaminase & guanine degradation & \\ _saprA_ & glyceraldehyde-3-phosphate dehydrogenase A & glycolysis & \\ \hline \hline \end{tabular}
* Reactive Oxygen Species.  
\end{table}