Figure 8: Working model for the role of Hfq in the regulation of adhesins in Y. enterocolitica.

The production of adhesins (in orange) is controlled by the RNA chaperone Hfq through its influence on transcriptional regulators (in blue) and through post-transcriptional inhibition (action on the grey arrows). We hypothesize that Hfq acts in concert with different cofactors (boxed), likely sRNAs, to exert its post-transcriptional effects on the different adhesins. Hfq represses expression of myfA (only when bacteria are grown at low pH) at the post-transcriptional level in logarithmic phase and through an effect on myfA transcription at 27 °C (in stationary phase). Production of Ail is controlled by Hfq at the post-transcriptional level at 37 °C. Hfq exerts a complex influence on YadA production, independently of VirF, the major direct transcriptional activator of yadA: (i) At 27 °C, Hfq promotes expression of yadA, possibly at the transcriptional level through its effect on the direct transcriptional repressor OmpR; (ii) conversely with the help of an unknown cofactor produced at 37 °C in stationary phase, Hfq represses yadA post-transcriptionally, (iii) ultimately, through its impact on proteases, like the periplasmic DegP, Hfq might also control YadA protein stability. Hfq controls the expression ompR and rovA which encode two of the four DNA-binding proteins that directly regulate invA. Finally, production of OmpX is negatively controlled by Hfq through its concerted effects on the transcriptional regulators RovA and OmpR and on the post-transcriptional level in coherent feed-forward loops. Black lines represent a reported direct regulation, such as the direct binding of a transcriptional regulator of the gene promoter (e.g. RovA and OmpR on the promoter region of invA) or the direct interaction of YadA with the protease DegP.