ASD proteins and ASD proteins containing the ZAS motif are predicted to bind specifically to σs and inhibit their activities [25–28]. The strictly human pathogen Neisseria meningitidis colonizes the nasopharynx of approximately 10 to 30% of the population. In

rare instances colonization results in invasive disease leading to life-threatening septicemia and meningitis [30]. Meningococci possess a variety of genes involved in adaptation to specific changes in the environment encountered in the host [31–36]. In addition to nutrient limitation, meningococci are also exposed to massive amounts of reactive oxygen species produced by host defenses [37, 38]. Fine tuning expression of genes required to survive hostile growth conditions is check details a prerequisite for the meningococcus to establish disease. All four publicly available, completely sequenced genomes of N. meningitidis contain a gene (NMA0233, NMB2144, NMC2123 and NMCC˜2103)

encoding a protein with homology to σE, the σ factor involved in stress responses [39–42]. In this study we explored the σE regulon of N. meningitidis. In addition, we provide evidence that the expression of σE (encoded by NMB2144) in meningococci is autoregulated and that its activity is under control of a protein encoded directly downstream of rpoE. This protein, encoded by NMB2145, is structurally related to ASD proteins and contains the ZAS motif (His30x3Cys34x2Cys37). We demonstrate that the Cys residues in the ZAS motif, as well as a Cys on

position 4, are important (Cys4 and C37) or essential (Cys34) for anti-σE activity of NMB2145. Results Vorinostat The gene cluster containing rpoE is transcribed as a polycistronic operon and transcriptionally regulated by σE In many bacterial species, rpoE is part of an autoregulated polycistronic operon also encoding its cognate anti-sigma factor [25–28]. In meningococci, NMB2144 is annotated as rpoE, encoding a protein with a molecular weight of approximately 23 kDa, 98% identical to the σE orthologue of N. gonorrhoeae [24] and 28% identical to σE of E. coli. Meningococcal rpoE is part of a ˜3 kb cluster of genes NMB2140 through NMB2145 (Fig.1a) having Etoposide a genomic arrangement similar to that found in N. gonorrhoeae [24]. All genes, except NMB2144, are annotated as hypothetical proteins. The minimal spacing found in the cluster suggests co-transcription of its genes. Figure 1 Transcriptional analysis of the NMB2140-NMB2145 region. A) Schematic representation of the organization of the NMB2140-NMB2145 region. Genes are indicated as open arrows that show the orientation and relative sizes of the putative ORFs. Primers used in RT-PCR are indicated by closed arrows. Sizes of calculated RT-PCR products are indicated below the black lines. The bent arrow indicates the promoter. B) RpoE is cotranscribed in the polycistronic operon NMB2140-2145 upon overexpressing of rpoE.