An RNA-dependent mechanism for transient expression of bacterial translocation filaments

Nucleic Acids Res. 2018 Apr 20;46(7):3366-3381. doi: 10.1093/nar/gky096.


The prokaryotic RNA chaperone Hfq mediates sRNA-mRNA interactions and plays a significant role in post-transcriptional regulation of the type III secretion (T3S) system produced by a range of Escherichia coli pathotypes. UV-crosslinking was used to map Hfq-binding under conditions that promote T3S and multiple interactions were identified within polycistronic transcripts produced from the locus of enterocyte effacement (LEE) that encodes the T3S system. The majority of Hfq binding was within the LEE5 and LEE4 operons, the latter encoding the translocon apparatus (SepL-EspADB) that is positively regulated by the RNA binding protein, CsrA. Using the identified Hfq-binding sites and a series of sRNA deletions, the sRNA Spot42 was shown to directly repress translation of LEE4 at the sepL 5' UTR. In silico and in vivo analyses of the sepL mRNA secondary structure combined with expression studies of truncates indicated that the unbound sepL mRNA is translationally inactive. Based on expression studies with site-directed mutants, an OFF-ON-OFF toggle model is proposed that results in transient translation of SepL and EspA filament assembly. Under this model, the nascent mRNA is translationally off, before being activated by CsrA, and then repressed by Hfq and Spot42.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Translocation / genetics*
  • Binding Sites / genetics
  • Cytoskeleton / genetics
  • Escherichia coli / genetics
  • Escherichia coli Proteins / genetics*
  • Gene Expression Regulation, Bacterial / radiation effects
  • Host Factor 1 Protein / genetics*
  • Nucleic Acid Conformation / radiation effects
  • Phosphoproteins / genetics*
  • RNA / genetics
  • RNA, Messenger / genetics
  • RNA, Messenger / radiation effects
  • RNA-Binding Proteins / genetics*
  • Repressor Proteins / genetics*
  • Type III Secretion Systems / genetics
  • Type III Secretion Systems / radiation effects
  • Ultraviolet Rays


  • CsrA protein, E coli
  • Escherichia coli Proteins
  • EspA protein, E coli
  • Hfq protein, E coli
  • Host Factor 1 Protein
  • LEE protein, E coli
  • Phosphoproteins
  • RNA, Messenger
  • RNA-Binding Proteins
  • Repressor Proteins
  • SepL protein, E coli
  • Type III Secretion Systems
  • RNA