PhoP induces RyjB expression under acid stress in Escherichia coli.

Bacterial small RNAs (sRNAs) play a pivotal role in post-transcriptional regulation of gene expression and participate in many physiological circuits. An ~80-nt-long RyjB was earlier identified as a novel sRNA, which appeared to be accumulated in all phases of growth in Escherichia coli. We have taken a comprehensive approach in the current study to understand the regulation of ryjB expression under normal and pH stress conditions. RpoS was not necessary for ryjB expression neither at normal condition nor under acid stress. Hfq also emerged to be unnecessary for RyjB accumulation. Interestingly, RyjB was detected as a novel acid stress induced sRNA. A DNA binding protein PhoP, a component of PhoP/Q regulon, was found to regulate ryjB expression at low pH, as the elimination of phoP allele in the chromosome exhibited a basal level of RyjB expression under acid stress. Ectopic expression of PhoP in ΔphoP cells restored the overabundance of RyjB in the cell. Overexpression of RyjB increased the abundance of sgcA transcripts, with which RyjB shares a 4-nt overlap. The current study increases our knowledge substantially regarding the regulation of ryjB expression in E. coli cell.