Noncoding regulatory RNA molecules, also known as small RNAs, participate in several bacterial regulatory networks. The central component of the carbon storage regulator (Csr) and the homologous repressor of secondary metabolites (Rsm) systems is an RNA binding protein (CsrA or RsmA) that regulates gene expression post-transcriptionally by affecting ribosome binding and/or mRNA stability. Members of the CsrB family of noncoding regulatory RNA molecules contain multiple CsrA binding sites and function as CsrA antagonists by sequestering this protein. Depending on the particular organism, the Csr (or Rsm) system participates in global regulatory circuits that control central carbon flux, the production of extracellular products, cell motility, biofilm formation, quorum sensing and/or pathogenesis.
"In Bacillus spp., RsaE (similar to CsrA) is involved in translation initiation of the gene hag coding for flagellin, while the protein FliW sequesters it by binding to CsrA, thus preventing CsrA activity (Romeo et al. 2013). Members of the CsrB family of noncoding regulatory RNA molecules contain multiple CsrA binding sites and function as CsrA antagonists by sequestering this protein (Babitzke and Romeo 2007, Romeo et al. 2013). "
[Show abstract][Hide abstract] ABSTRACT: The review recapitulate the current knowledge on the roles and importance of non-coding RNAs (ncRNAs) and small RNAs in bacteria. Many new RNAs have been described either in Gram positive and Gram negative bacteria, and in particular RNAs involved in pathogenesis and tolerance to stresses. The review recapitulate the current knowledge on the roles and importance of non-coding RNAs (ncRNAs) and small RNAs in bacteria. Several cases of regulating and signaling RNAs are presented either in Gram positive and Gram negative bacteria, with a focus on bacterial RNAs involved in pathogenesis and stress responses. Examples of small RNAs and their mechanisms of action, transcriptional and post-transcriptional regulation, induction of new genes, increased stability of their targets or their destination to the degradation pathway.
"Similar to their Gram-negative counterparts, most sRNAs from Gram-positive species range from 50 to 250 nucleotides in length and, with notable exceptions (Balaban and Novick, 1995; Gimpel et al., 2010), do not encode for any proteins; rather, the RNA molecules themselves have intrinsic regulatory activity. For the most part, given the absence of the regulator-protein sequestering CsrB-like sRNAs from Gram-positive genomes (Babitzke and Romeo, 2007), sRNAs from Gram-positive organisms fulfil their regulatory activity by base-pairing to one or more target mRNAs, leading to an alteration in the stability and/or translation of the hybridized mRNAs. "
[Show abstract][Hide abstract] ABSTRACT: RNA-based mechanisms of regulation represent a ubiquitous class of regulators that are associated with diverse processes including nutrient sensing, stress response, modulation of horizontal gene transfer, and virulence factor expression. While better studied in Gram-negative bacteria, the literature is replete with examples of the importance of RNA-mediated regulatory mechanisms to the virulence and fitness of Gram-positives. Regulatory RNAs are classified as cis-acting, e.g. riboswitches, which modulate the transcription, translation, or stability of co-transcribed RNA, or trans-acting, e.g. small regulatory RNAs, which target separate mRNAs or proteins. The group A Streptococcus (GAS, Streptococcus pyogenes) is a Gram-positive bacterial pathogen from which several regulatory RNA mechanisms have been characterized. The study of RNA-mediated regulation in GAS has uncovered novel concepts with respect to how small regulatory RNAs may positively regulate target mRNA stability, and to how CRISPR RNAs are processed from longer precursors. This review provides an overview of RNA-mediated regulation in Gram-positive bacteria, and is highlighted with specific examples from GAS research. The key roles that these systems play in regulating bacterial virulence are discussed and future perspectives outlined.
"The key regulators of CsrA activity are CsrB-like sRNAs which act as decoys of the protein. These sRNAs, of which many bacteria encode more than one copy, carry multiple high-affinity sites containing the GGA motif and thereby titrate CsrA away from its target mRNAs (Babitzke and Romeo, 2007). "
[Show abstract][Hide abstract] ABSTRACT: Enteric pathogens often cycle between virulent and saprophytic lifestyles. To endure these frequent changes in nutrient availability and composition bacteria possess an arsenal of regulatory and metabolic genes allowing rapid adaptation and high flexibility. While numerous proteins have been characterized with regard to metabolic control in pathogenic bacteria, small non-coding RNAs have emerged as additional regulators of metabolism. Recent advances in sequencing technology have vastly increased the number of candidate regulatory RNAs and several of them have been found to act at the interface of bacterial metabolism and virulence factor expression. Importantly, studying these riboregulators has not only provided insight into their metabolic control functions but also revealed new mechanisms of post-transcriptional gene control. This review will focus on the recent advances in this area of host-microbe interaction and discuss how regulatory small RNAs may help coordinate metabolism and virulence of enteric pathogens.
Frontiers in Cellular and Infection Microbiology 07/2014; 4:91. DOI:10.3389/fcimb.2014.00091 · 3.72 Impact Factor
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