This was confirmed by our observation that membrane stress did not alter σE activity. However, as mentioned before, the majority GDC-0449 chemical structure of σE dependent proteins are expressed at low levels [61], which might be below the detection limit

of the assay used in this study. As it is much easier to detect small changes in the transcriptome comparing ΔrpoE (σE knock out) or H44/76 + pNMB2144 (σE overexpression) with H44/76 (wt strain), we are planning those experiments. The recent identification in N. meningitidis of an sRNA controlling a gene and functional Hfq facilitating the interaction between sRNA and target mRNA, suggests the existence of a ribo-regulated network in this pathogen [62–65]. In many other species links between the σE regulon and the ribo-regulated network exist

[66–71], but in meningococci this is as yet unexplored. The genetic organization of the rpoE operon (NGO1948 through NGO1943) of N. gonorrhoeae is identical to that of meningococci (NMB2140-NMB2145), and four genes, NGO1946, NGO1947, NGO1948 belonging to the rpoE operon, and NGO2059, IWP-2 chemical structure encoding MsrA/MrsB, were also upregulated, along with σE (NGO1944) itself, in a gonococcal strain overexpressing rpoE [24]. We demonstrated cotranscription of all genes in the meningococcal rpoE operon. The function of proteins encoded by NMB2140-NMB2143 is currently unknown. NMB2140 might encode a protein with possible trans membrane domains and contains motifs

found in the DoxX/D-like family, involved in oxidation of sulfur [72, 73]. NMB2141 through NMB2143 encode hypothetical proteins of unknown function. Based on the structural relatedness of NMB2145 to ASD proteins [26] and sequence conservation of Cys residues shown to be essential for anti-σR activity of RsrA of S. coelicolor [29] we argue that NMB2145, directly downstream of and co-transcribed with rpoE, encodes the anti-σE factor. Indeed, upon deletion of NMB2145, msrA/msrB, which we demonstrated to Phospholipase D1 be transcriptionally controlled by σE, was abundantly expressed. Irrefutable evidence for a functional interaction of NMB2145 with σE was obtained by the substitution of Cys residues with Ala at positions in NMB2145 that correspond to Cys residues in RsrA. We found that Cys34 of NMB2145 is essential and, albeit to a lesser extent, Cys4 and Cys37 are also required for optimal anti-σE activity of NMB2145. We therefore suggest annotating NMB2145 as MseR, Meningococcal sigmaE Regulator. RsrA is a STA-9090 molecular weight metalloprotein, containing near-stoichiometric amounts of Zn2+ [29]. Oxidation induces a disulphide bond between two of the Zn2+ ligands (Cys11 and Cys44) resulting in loss of Zn2+ and dissociation of the σR-RsrA-complex, thereby allowing σR transcription. Thioredoxin is able to reduce oxidized RsrA, and the induction of expression of thioredoxin itself is σR dependent, suggesting that σR, RsrA and the thioredoxin system in S.