Regulation of an RNA toxin-antitoxin system, SdsR-RyeA, by a small RNA GcvB.

The toxin-antitoxin (TA) system regulates many physiological processes in free-living bacteria. One such TA system in Escherichia coli comprises an RNA toxin SdsR and an antitoxin RyeA. An overabundance of SdsR is toxic to the cells. RyeA normalizes SdsR abundance and helps the cells to adapt to altered conditions. The current study showed that a novel small RNA (sRNA) regulator GcvB directly interacts with RyeA to maintain its abundance in the cells under normal or low pH conditions. The deletion of the gcvB allele in the E. coli chromosome resulted in a ∼3-fold decrease in intrabacterial RyeA accumulation. An ectopic expression of GcvB in ΔgcvB strain reinstated RyeA abundance to its normal level. Induction of GcvB in the cells upon exposure to low pH resulted in a simultaneous increase in intracellular RyeA. While GcvB increases RyeA abundance in the cells, SdsR accumulation is divergently regulated by GcvB. The absence of the gcvB gene in E. coli leads to upregulation of SdsR and vice versa. The GcvB-mediated decrease of SdsR accumulation stems from the increased RyeA-driven normalization of SdsR. This study delineates a novel mechanism for the regulation of the expression of an RNA toxin SdsR by another sRNA regulator GcvB through a feed-forward control.