Role of the conserved cysteines C131 and C181 of CC3252 upon expression of σF-dependent genes. A. The deduced protein sequences of orthologs of CC3252 obtained from Cupriavidus metallidurans (rme), Pseudomonas entomophila (pen), Pseudomonas putida (ppu), Rhizobium leguminosarum (rlg), Maricaulis maris (mmr) and Sinorhizobium meliloti were compared with CC3252 deduced protein sequence of Caulobacter crescentus (ccr) using MultiAlign . Arrows assign the conserved cysteines C131 and C181 of C. crescentus in all orthologs. B. Illustration of the putative topology of the deduced protein sequence encoded by CC3252 on the inner membrane. The six transmembrane segments were predicted using SMART  and are indicated by green cylinders. Conserved cysteine residues and denoted as red circles. C. qRT-PCR was performed using total RNA extracted from exponential growth phase cells from parental strain NA1000 and mutant strains SG22 (C131S), SG23 (C181S) and SG24 (C131S-181S) cultured under unstressed condition (no stress) or following exposure to 55 μM potassium dichromate (K2Cr2O7) for 30 min. Values represent the fold increase of CC2748, CC2906, CC3255, CC3252 and CC3253 (sigF) expression in the corresponding strains exposed or not to the stress condition compared with that of the parental strain NA1000 growing under no stress conditions. Results were normalized using gene CC0088 as the endogenous control, which was constitutively expressed in the samples analyzed. Data are mean values of two independent experiments; bars represent the standard error. Statistical analysis is shown in Additional file 1: Table S4.