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J. Bacteriol., 07 1996, 3763-3770, Vol 178, No. 13
L Brown and T Elliott
The RpoS transcription factor (also called sigma Sor sigma 38) is required
for the expression of a number of stationary-phase and osmotically
inducible genes in Escherichia coli. RpoS is also a virulence factor for
several pathogenic bacteria, including Salmonella typhimurium. The activity
of RpoS is regulated in response to several different signals, at the
transcriptional and translational levels as well as by proteolysis. Here we
report that host factor I (HF-I), the product of the hfq gene, is required
for efficient expression of rpoS in S. typhimurium. HF-I is a small,
heat-stable, site-specific RNA- binding protein originally characterized
for its role in replication of the RNA bacteriophage Q beta of E. coli. Its
role in the uninfected bacterial cell has previously been unknown. Assays
of Beta- galactosidase in strains with rpoS-lac fusions, Western blot
(immunoblot) analysis, and pulse-labeling and immunoprecipitation of both
fusion proteins and native RpoS show that an S. typhimurium hfq mutant has
a four- to sevenfold reduction in expression of rpoS that is attributable
primarily to a defect in translation. These results add a new level of
complexity to the regulation of RpoS activity.
Copyright © 1996, American Society for Microbiology
Efficient translation of the RpoS sigma factor in Salmonella typhimurium requires host factor I, an RNA-binding protein encoded by the hfq gene
Department of Microbiology and Immunology, West Virginia University Health Sciences Center, Morgantown, West Virginia 26506, USA.
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