Abstract
Bacteria adapt to the different environments encountered by rapid and tightly controlled regulations involving complex networks. A first line of control is transcriptional with regulators such as two-component systems (TCSs) that respond to physical and chemical perturbations. It is followed by posttranscriptional regulations in which small regulatory RNAs (sRNAs) may affect RNA translation. Streptococci are opportunistic pathogens for humans and farm animals. The TCS CiaRH is highly conserved among this genus and crucial in bacterial survival under stressful conditions. In several streptococcal species, some sRNAs belong to the CiaRH regulon and are called csRNAs for cia-dependent sRNAs. In this review, we start by focusing on the Streptococcus species harboring a CiaRH TCS. Then the role of CiaRH in streptococcal pathogenesis is discussed in the context of recent studies. Finally, we give an overview of csRNAs and their functions in Streptococci with a focus on their importance in bacterial adaptation and virulence.
Highlights
Due to their importance in the regulation of gene expression, small non-coding regulatory RNAs are present in all kingdoms of life
The aim of this review is to carry out an inventory of the small regulatory RNAs (sRNAs) regulated by the two-component regulatory system CiaRH present in streptococci
The ciadependent sRNAs (csRNAs) increase the regulatory networks of CiaR, which already directly controls csRNAs in Streptococci more than 20 other genes (Halfmann et al, 2007)
Summary
Due to their importance in the regulation of gene expression, small non-coding regulatory RNAs (sRNAs) are present in all kingdoms of life. A decade ago, the high number of sRNAs discovered in various bacterial species was surprising (Brantl, 2009). These sRNAs differ in length, structure, and mode of action (Gottesman and Storz, 2011). SRNAs, 50–500 nucleotides long molecules, are often involved in the regulation of several cellular pathways and allow bacteria to adapt and survive under stressful conditions. In 1984, the first chromosomally encoded sRNA was discovered in Escherichia coli: MicF. This sRNA inhibits the translation of OmpF messenger RNA (mRNA) encoding the major membrane porin, OmpF (Mizuno et al, 1984). To respond to environmental changes, bacteria must first sense these changes, and two-component regulatory systems (TCS) are known to perform this function (Stock et al, 2000)
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