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Enteropathogenic Escherichia coli, commonly known as EPEC is a diarrheal pathogen that infects infants in developing countries.
The bacterium belongs to the attaching and effacing (A/E) morphotype of pathogenic E. coli, since it infects infants by directly
binding to intestinal epithelial cells and destroying the microvilli. The virulence of EPEC is attributed to its major pathogenicity
island: The locus of enterocyte effacement (LEE). Treatment of EPEC infections is particularly challenging, because currently there
are no vaccines against this bacterium. The problem is only exacerbated by the emergence of multi-drug resistant strains of EPEC.
Thus, understanding the regulatory pathways that govern the LEE is critical towards the development of effective measures to
combat EPEC infections. The LEE is responsive to a myriad of environmental cues with the majority of them targeting three LEEencoded
transcription factors: Ler, GrlR, and GrlA. Whereas transcriptional regulation of the LEE has been widely characterized,
post transcriptional regulation including regulation by trans-encoded regulatory small RNAs (sRNAs), remains understudied. Most
sRNAs exert their effects by directly base-pairing to their target mRNAs to influence the translation and/or stability of the target
mRNA. A subset of these sRNAs requires Hfq, a chaperone protein that assists in the finding and base-pairing of sRNAs to their target
mRNAs. One such sRNA is RyhB. Preliminary results suggest that Hfq and RyhB core press the grlRA mRNA that encodes GrlR and
GrlA. To better understand the mechanism of action of RyhB on the grlRA mRNA, we preformed in silico alignment analysis. By
using IntaRNA, we identified regions of complementarity between RyhB and the ribosomal binding site, in the 5’ untranslated region
(UTR), of the upstream gene grlR in the grlRA mRNA. In order to confirm this prediction of direct base-pairing between RyhB and
grlRA, we constructed a polynucleotide mutation in the seed region of RyhB; this mutation completely abolished the ability of the
mutant RyhB to base pair to and represses the grlR-lacZ fusion. Thus, collectively, our results suggest that RyhB represses the LEE by
directing base-pairing to the leader segment of the grlRA mRNA and preventing the expression of both GrlR and GrlA. Future studies
are aimed at further understanding the RyhB-mediated regulation of the LEE by genetic, biochemical and phenotypic assays to with
the goal of developing efficacious and potent pharmacological targets against EPEC.
Marisa Egan is affiliated to Saint Joseph’s University, USA.