Effects of the Global Regulator CsrA on the BarA/UvrY Two-Component Signaling System

Abstract

The hybrid sensor kinase BarA and its cognate response regulator UvrY, members of the two-component signal transduction family, activate transcription of CsrB and CsrC noncoding RNAs. These two small RNAs act by sequestering the RNA binding protein CsrA, which posttranscriptionally regulates translation and/or stability of its target mRNAs. Here, we provide evidence that CsrA positively affects, although indirectly, uvrY expression, at both the transcriptional and translational levels. We also demonstrate that CsrA is required for properly switching BarA from its phosphatase to its kinase activity. Thus, the existence of a feedback loop mechanism that involves the Csr and BarA/UvrY global regulatory systems is exposed. The BarA/UvrY two-component signal transduction system (TCS) of Escherichia coli consists of the membrane-bound sensor kinase BarA and its cognate response regulator UvrY (1). BarA, which belongs to the subfamily of tripartite sensor kinases (2, 3), senses and responds to the presence of formate and acetate but also to that of other short-chain fatty acids (4). Phosphorylated BarA catalyzes the transphosphorylation of UvrY (1), a typical response regulator of the FixJ family (1, 5), which in turn activates expression of the noncoding RNAs of the carbon storage regulation (Csr) system, CsrB and CsrC. These small regulatory RNAs possess repeated sequence elements that allow them to interact with multiple copies of the RNA binding protein CsrA and thereby prevent its regulatory interaction with its mRNA targets (6).CsrA is a small, dimeric RNA binding protein that coordinates gene expression by positively or negatively regulating the translation, stability, and/or elongation of its target transcripts (7,8). CsrA directly interacts with the 5= untranslated leaders of target mRNAs at sites characterized by a GGA sequence that is often located within the loop of a short stem-loop structure (9-11). In this way, CsrA activates exponential-phase processes while it represses several stationary-phase functions (12). CsrA is widely distributed among eubacteria (13) and regulates expression of genes for virulence factors (14, 15), quorum sensing (16, 17), motility (18,19), carbon metabolism (20, 21), biofilm formation (22, 23), cyclic di-GMP synthesis (24), and peptide uptake (10).Curiously, activation of csrB transcription, which depends directly on UvrY-P, does not take place in a csrA mutant strain (25). Therefore, it has been suggested that CsrA has a positive effect on the BarA/UvrY TCS. In this study, we confirmed and extended these results by examining the effects of CsrA on either the expression or the activity of BarA and UvrY. Our results demonstrate that CsrA, apparently indirectly, is required for proper uvrY expression and also for activation of the BarA kinase activity. MATERIALS AND METHODSBacterial strains, plasmids, and growth conditions. The strains and plasmids used in this work are listed in csrB-lacZ) construction, the barA gene was deleted by homologous recombination using the lambda Red ...

Global Regulation by CsrA and Its RNA Antagonists

“…Disruption of csrD stabilizes CsrB/C, causing sequestration of CsrA. Because CsrA activates csrB/C transcription (82, 90, 95), this causes csrB-lacZ transcription to decrease. Unlike CsrB/C RNA, lacZ mRNA stability is not affected by CsrD, thus in the csrD mutant csrB-lacZ expression is decreased.…”

“…This indirect activation occurs via positive effects of CsrA on uvrY expression and the ability to cause BarA to switch from its phosphatase to kinase activity (90). The negative feedback loop that this creates in the Csr system allows CsrB and CsrC to mediate compensatory effects on each other’s expression (40, 94) (Fig.…”

Circuitry Linking the Catabolite Repression and Csr Global Regulatory Systems of Escherichia coli

“…Transcription of both csrB and csrC (csrB/C) is activated by the BarA-UvrY two-component signal transduction system (TCS) in response to carboxylic acids such as formate and acetate (3,(36)(37)(38)(39)(40)(41). CsrA indirectly activates transcription of CsrB and CsrC through its effects on BarA-UvrY, creating a negative-feedback loop within the Csr circuitry (37,38,42). CsrB/C turnover requires the GGDEF-EAL domain protein CsrD, which is necessary for cleavage by RNase E and turnover (42,43).…”

Identification by PCR signature-tagged mutagenesis of attenuated Salmonella Pullorum mutants and corresponding genes in a chicken embryo model

“…The uvrY gene encodes a DNA-binding response regulator of the BarA/UvrY two-component regulatory system, which responds to short chain carboxylates [16,17]. The hybrid sensor kinase BarA and its cognate response regulator UvrY, members of the two-component signal transduction family [18,19], activate transcription of CsrB and CsrC noncoding RNAs [20]. UvrY can regulate biofilm formation, motility and virulence determinants in uropathogenic E. coli.…”