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Journal of Bacteriology, March 2001, p. 1997-2005, Vol. 183, No. 6
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.6.1997-2005.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Hfq Is Necessary for Regulation by the Untranslated RNA DsrA

Darren D. Sledjeski,1,* Christina Whitman,1,dagger and Aixia Zhang2

Department of Microbiology and Immunology, Medical College of Ohio, Toledo, Ohio, 43614,1 and Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 208922

Received 16 August 2000/Accepted 8 January 2001

DsrA is an 85-nucleotide, untranslated RNA that has multiple regulatory activities at 30°C. These activities include the translational regulation of RpoS and H-NS, global transcriptional regulators in Escherichia coli. Hfq is an E. coli protein necessary for the in vitro and in vivo replication of the RNA phage Qbeta . Hfq also plays a role in the degradation of numerous RNA transcripts. Here we show that an hfq mutant strain is defective for DsrA-mediated regulation of both rpoS and hns. The defect in rpoS expression can be partially overcome by overexpression of DsrA. Hfq does not regulate the transcription of DsrA, and DsrA does not alter the accumulation of Hfq. However, in an hfq mutant, chromosome-expressed DsrA was unstable (half-life of 1 min) and truncated at the 3' end. When expressed from a multicopy plasmid, DsrA was stable in both wild-type and hfq mutant strains, but it had only partial activity in the hfq mutant strain. Purified Hfq binds DsrA in vitro. These results suggest that Hfq acts as a protein cofactor for the regulatory activities of DsrA by either altering the structure of DsrA or forming an active RNA-protein complex.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Medical College of Ohio, 3055 Arlington Ave., Toledo, OH 43614-5806. Phone: (419) 383-5192. Fax: (419) 383-3002. E-mail: dsledjeski{at}mco.edu.

dagger Present address: Bio-Rad Laboratories, Life Science Group, Hercules, CA 94547.

Journal of Bacteriology, March 2001, p. 1997-2005, Vol. 183, No. 6
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.6.1997-2005.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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