Regulation of RpoS levels and activity by YmdB. (A) Effect of YmdB on in vivo expression levels of RpoS. KS004 [SG30013 (λRpoS750::LacZ]  strains containing either pCA24N (−gfp) or ASKA-ymdB (−) were grown to OD600 = 0.2, induced by IPTG (0.1 mM final), and further grown to OD600 = 1.0. Aliquots were then assayed for β-galactosidase activity. Data represent the mean values from n = 3 experiments (p = 0.05). (B) Expression level of RpoS. Total lysates prepared from the cell described in (A) and from Keio-∆rpoS cells were immunoblotted antibodies against RpoS and S1. The Keio-∆rpoS strain is included to show the specificity of the antibody. The relative levels of RpoS normalized against S1 protein are shown. ND, not determined. (C) Determination of steady-state levels of rpoS transcript induced by YmdB. cDNA synthesized from total RNA obtained from BW25113, KSK002 (∆ymdB), KSK001 (rnc14) or BW25113 cells containing either pCA24N (−gfp) or ASKA-ymdB (−) were qPCR amplified using the rpoS- or 16S RNA-specific primer sets listed in Additional file 1: Table S2 and then compared. Data represent the mean values from triplicate experiments.