Analysis of CC3254 and sigF promoter activity. A. Illustration of the plasmid constructions used in β-galactosidase assays. Fragments containing the upstream region from CC3254 or sigF were obtained by PCR, sequenced and cloned into the plasmid placZ290 . Light gray boxes represent the −35 and −10 promoter elements determined by 5´RACE experiment (CC3254) or by primer extension experiments (sigF) . The black triangles correspond to the translation start sites. Numbers right and left indicate the position of 3’ and 5’ ends, respectively, relative to the transcription start site +1. B. β-galactosidase assays carried out with exponential growth phase cells from parental strain NA1000 (WT), sigF null mutant SG16 strain (ΔsigF) and sigF overexpressing cells (SigF++) containing the empty vector placZ290 or one of the different constructs with the upstream region of CC3254 or sigF. Data are mean values of three independent experiments; bars represent the standard error. Statistical analysis is shown in Additional file 1: Table S4.