Translational activation by the noncoding RNA DsrA involves alternative RNase III processing in the rpoS 5'-leader

Area of Science:

• Microbiology
• Molecular Biology
• RNA Biology

Background:

• The Escherichia coli rpoS gene encodes the sigmaS factor, crucial for stationary phase adaptation.
• Regulation of rpoS involves translational control by the small noncoding RNA DsrA.
• RNase III is an enzyme involved in RNA processing and degradation.

Purpose of the Study:

• To investigate the role of RNase III in rpoS mRNA stability and regulation.
• To elucidate the mechanism by which DsrA influences rpoS mRNA processing.
• To understand the dual function of DsrA in translational activation and mRNA processing.

Main Methods:

• Analysis of rpoS mRNA stability and sigmaS protein levels in wild-type and RNase III-deficient E. coli strains.
• In vivo detection of RNA decay intermediates.
• Mapping of RNase III cleavage sites in the rpoS leader sequence and in the rpoS/DsrA duplex.

Main Results:

• RNase III deficiency leads to increased rpoS mRNA stability and higher sigmaS protein concentrations.
• The in vitro mapped RNase III cleavage site in the rpoS leader is not detected in vivo, suggesting rapid inactivation.
• DsrA binding to rpoS mRNA creates an alternative RNase III cleavage site within the rpoS/DsrA duplex.

Conclusions:

• RNase III plays a critical role in the rapid inactivation of rpoS mRNA.
• DsrA's function extends beyond translational activation to include alternative mRNA processing via RNase III.
• This study reveals a novel regulatory mechanism involving small RNAs and RNase III in gene expression control.