A Novel Small RNA, DsrO, in Deinococcus radiodurans Promotes Methionine Sulfoxide Reductase () Expression for Oxidative Stress Adaptation

Reactive oxygen species (ROS) can cause destructive damage to biological macromolecules and protein dysfunction in bacteria. Methionine sulfoxide reductase (Msr) with redox-active Cys and/or seleno-cysteine (Sec) residues can restore physiological functions of the proteome, which is essential for oxidative stress tolerance of the extremophile Deinococcus radiodurans. However, the underlying mechanism regulating MsrA enzyme activity in D. radiodurans under oxidative stress has remained elusive. Here, we identified the function of MsrA in response to oxidative stress. expression in D. radiodurans was significantly upregulated under oxidative stress. The mutant showed a deficiency in antioxidative capacity and an increased level of dabsyl-Met-S-SO, indicating increased sensitivity to oxidative stress. Moreover, mRNA was posttranscriptionally regulated by a small RNA, DsrO. Analysis of the molecular interaction between DsrO and mRNA demonstrated that DsrO increased the half-life of mRNA and then upregulated MsrA enzyme activity under oxidative stress compared to the wild type. expression was also transcriptionally regulated by the DNA-repairing regulator DrRRA, providing a connection for further analysis of protein restoration during DNA repair. Overall, our results provide direct evidence that DsrO and DrRRA regulate expression at two levels to stabilize mRNA and increase MsrA protein levels, revealing the protective roles of DsrO signaling in D. radiodurans against oxidative stress. The repair of oxidized proteins is an indispensable function allowing the extremophile D. radiodurans to grow in adverse environments. Msr proteins and various oxidoreductases can reduce oxidized Cys and Met amino acid residues of damaged proteins to recover protein function. Consequently, it is important to investigate the molecular mechanism maintaining the high reducing activity of MsrA protein in D. radiodurans during stresses. Here, we showed the protective roles of an sRNA, DsrO, in D. radiodurans against oxidative stress. DsrO interacts with mRNA to improve mRNA stability, and this increases the amount of MsrA protein. In addition, we also showed that DrRRA transcriptionally regulated gene expression. Due to the importance of DrRRA in regulating DNA repair, this study provides a clue for further analysis of MsrA activity during DNA repair. This study indicates that protecting proteins from oxidation is an effective strategy for extremophiles to adapt to stress conditions.