Regulatory Interactions of Csr Components: the RNA Binding Protein CsrA Activates csrB Transcription in Escherichia coli

Abstract

The global regulator CsrA (carbon storage regulator) of Escherichia coli is a small RNA binding protein that represses various metabolic pathways and processes that are induced in the stationary phase of growth, while it activates certain exponential phase functions. Both repression and activation by CsrA involve posttranscriptional mechanisms, in which CsrA binding to mRNA leads to decreased or increased transcript stability, respectively. CsrA also binds to a small untranslated RNA, CsrB, forming a ribonucleoprotein complex, which antagonizes CsrA activity. We have further examined the regulatory interactions of CsrA and CsrB RNA. The 5 end of the CsrB transcript was mapped, and a csrB::cam null mutant was constructed. CsrA protein and CsrB RNA levels were estimated throughout the growth curves of wild-type and isogenic csrA, csrB, rpoS, or csrA rpoS mutant strains. CsrA levels exhibited modest or negligible effects of these mutations. The intracellular concentration of CsrA exceeded the total CsrA-binding capacity of intracellular CsrB RNA. In contrast, CsrB levels were drastically decreased (ϳ10-fold) in the csrA mutants. CsrB transcript stability was unaffected by csrA. The expression of a csrB-lacZ transcriptional fusion containing the region from ؊242 to ؉4 bp of the csrB gene was decreased ϳ20-fold by a csrA::kanR mutation in vivo but was unaffected by CsrA protein in vitro. These results reveal a significant, though most likely indirect, role for CsrA in regulating csrB transcription. Furthermore, our findings suggest that CsrA mediates an intriguing form of autoregulation, whereby its activity, but not its levels, is modulated through effects on an RNA antagonist, CsrB.

Rapid and robust signaling in the CsrA cascade via RNA–protein interactions and feedback regulation

“…Specifically, we sought to determine whether putative transcriptional and translational feedback loops described in the native system affect signaling dynamics under our experimental conditions (7,23). Feedback is known to influence signaling dynamics (1) and CsrA has been reported to (i) positively and negatively regulate its own expression via mechanisms that have not been fully elucidated (23), (ii) inhibit its own activity by increasing transcription of CsrB and CsrC (10,24), and (iii) inhibit its own activity by decreasing CsrD production, which increases CsrB (25).…”

A Repeated GGA Motif Is Critical for the Activity and Stability of the Riboregulator RsmY of Pseudomonas fluorescens

“…Such a phenomenon has been described in E. coli for the Hfq protein, which stabilizes spot 42 RNA, an antisense riboregulator involved in regulation of the gal operon (6). In Erwinia carotovora subspecies carotovora, the absence of the RsmA protein also results in a marked reduction of RsmB RNA halflife (46), whereas the E. coli homolog CsrA fails to show a comparable effect on the stability of CsrB RNA (47). In P. fluorescens strain CHA0, which encodes a second RsmA-like protein (RsmE) (13), the situation, may even be more complex.…”

The LetE Protein Enhances Expression of Multiple LetA/LetS-Dependent Transmission Traits by Legionella pneumophila

“…Transformants were isolated, colony purified, and cultured overnight on Kornberg medium containing 200 M IPTG (isopropyl-␤-D-thiogalactopyranoside). Intracellular glycogen accumulation was visualized with iodine vapor by inverting plates over iodine crystals (15).…”

“…When indicated, gentamicin was added to a final concentration of 10 g per ml. E. coli strains MG1655, TR1-5 MG1655 (csrA::kanR), and RG1-B MG1655 (csrB::cam) were grown on Kornberg medium (15).…”