sRNA-mediated RNA processing regulates bacterial cell division

Tight control of cell division is essential for survival of most organisms. For prokaryotes, the regulatory mechanisms involved in the control of cell division are mostly unknown. We show that the small non-coding sRNA StsR has an important role in controlling cell division and growth in the alpha-proteobacterium Rhodobacter sphaeroides. StsR is strongly induced by stress conditions and in stationary phase by the alternative sigma factors RpoHI/HII, thereby providing a regulatory link between cell division and environmental cues. Compared to the wild type, a mutant lacking StsR enters stationary phase later and more rapidly resumes growth after stationary phase. A target of StsR is UpsM, the most abundant sRNA in the exponential phase. It is derived from partial transcriptional termination within the 5' untranslated region of the mRNA of the division and cell wall (dcw) gene cluster. StsR binds to UpsM as well as to the 5' UTR of the dcw mRNA and the sRNA-sRNA and sRNA-mRNA interactions lead to a conformational change that triggers cleavage by the ribonuclease RNase E, affecting the level of dcw mRNAs and limiting growth. These findings provide interesting new insights into the role of sRNA-mediated regulation of cell division during the adaptation to environmental changes.