Mol. Cells 2019; 42(5): 426~439  https://doi.org/10.14348/molcells.2019.0040
Mechanisms for Hfq-Independent Activation of rpoS by DsrA, a Small RNA, in Escherichia coli
Wonkyong Kim, Jee Soo Choi, Daun Kim, Doohang Shin, Shinae Suk, and Younghoon Lee*
Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
Received March 8, 2019; Accepted March 11, 2019.; Published online April 19, 2019.
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ABSTRACT
Many small RNAs (sRNAs) regulate gene expression by base pairing to their target messenger RNAs (mRNAs) with the help of Hfq in Escherichia coli. The sRNA DsrA activates translation of the rpoS mRNA in an Hfq-dependent manner, but this activation ability was found to partially bypass Hfq when DsrA is overproduced. The precise mechanism by which DsrA bypasses Hfq is unknown. In this study, we constructed strains lacking all three rpoS-activating sRNAs (i.e., ArcZ, DsrA, and RprA) in hfq+ and Hfq- backgrounds, and then artificially regulated the cellular DsrA concentration in these strains by controlling its ectopic expression. We then examined how the expression level of rpoS was altered by a change in the concentration of DsrA. We found that the translation and stability of the rpoS mRNA are both enhanced by physiological concentrations of DsrA regardless of Hfq, but that depletion of Hfq causes a rapid degradation of DsrA and thereby decreases rpoS mRNA stability. These results suggest that the observed Hfq dependency of DsrA-mediated rpoS activation mainly results from the destabilization of DsrA in the absence of Hfq, and that DsrA itself contributes to the translational activation and stability of the rpoS mRNA in an Hfq-independent manner.
Keywords: DsrA, Escherichia coli, Hfq, rpoS, small RNAs
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