Identification of the genes directly controlled by the response regulator CiaR in Streptococcus pneumoniae: five out of 15 promoters drive expression of small non-coding RNAs.

The two-component regulatory system CiaRH of Streptococcus pneumoniae has been implicated in beta-lactam resistance, maintenance of cell integrity, competence and virulence, but the genes that are regulated directly by the system have not been defined. Using transcriptional mapping, in vitro CiaR binding, and in vivo analysis of CiaR-mediated regulation, 15 promoters were identified to be directly controlled by the response regulator CiaR. A direct repeat, TTTAAG-N5-TTTAAG, was found to be essential for CiaR binding and regulation. It is present, either completely or with subtle changes, in all promoter regions. Fourteen promoters of the regulon are activated by CiaR, and one was found to be controlled negatively. The genes that are transcribed from these promoters included ciaRH, loci that are predicted to be involved in the modification of teichoic acids (lic), in sugar metabolism (mal, man), stress response (htrA), chromosome segregation (parB), protease maturation (ppmA) and unknown functions. Remarkably, the five strongest promoters of the CiaR regulon drive expression of small RNAs. These small RNAs, designated csRNAs for cia-dependent small RNAs, are non-coding, between 87 and 151 nt in size, and show a high degree of similarity to each other. The analysis of deletion mutants in the csRNA genes revealed that csRNA4 and csRNA5 affect stationary-phase autolysis. The identification of five small non-coding regulatory RNAs opens new perspectives to approach the physiological role of the CiaRH two-component regulatory system.