Format

Send to

Choose Destination
Proc Natl Acad Sci U S A. 2011 Aug 2;108(31):12875-80. doi: 10.1073/pnas.1109379108. Epub 2011 Jul 18.

Small RNAs endow a transcriptional activator with essential repressor functions for single-tier control of a global stress regulon.

Author information

1
Department of Microbiology and Immunology, and Department of Cell and Tissue Biology, University of California, San Francisco, CA 94158, USA.

Abstract

The Escherichia coli σ(E) envelope stress response monitors and repairs the outer membrane, a function central to the life of Gram-negative bacteria. The σ(E) stress response was characterized as a single-tier activation network comprised of ~100 genes, including the MicA and RybB noncoding sRNAs. These highly expressed sRNAs were thought to carry out the specialized function of halting de novo synthesis of several abundant porins when envelope homeostasis was perturbed. Using a systematic target profiling and validation approach we discovered that MicA and RybB are each global mRNA repressors of both distinct and shared targets, and that the two sRNAs constitute a posttranscriptional repression arm whose regulatory scope rivals that of the protein-based σ(E) activation arm. Intriguingly, porin mRNAs constitute only ~1/3 of all targets and new nonporin targets predict roles for MicA and RybB in crosstalk with other regulatory responses. This work also provides an example of evolutionarily unrelated sRNAs that are coinduced and bind the same targets, but at different sites. Our finding that expression of either MicA or RybB sRNA protects the cell from the loss of viability experienced when σ(E) activity is inadequate illustrates the importance of the posttranscriptional repression arm of the response. σ(E) is a paradigm of a single-tier stress response with a clear division of labor in which highly expressed noncoding RNAs (MicA, RybB) endow a transcriptional factor intrinsically restricted to gene activation (σ(E)) with the opposite repressor function.

PMID:
21768388
PMCID:
PMC3150882
DOI:
10.1073/pnas.1109379108
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center