The CacA-dependent activation of the CpxR/CpxA requires functional thioredoxin 1. A. Alignment of the amino acid sequences of the CacA protein of S. enterica serovar Typhimurium LT2 (STM), C. koseri (CKO), E. coli (ECO), C. sakazakii (ESA), Enterobacter sp. 638 (ENT), Klebsiella pneumoniae (KPN), D. dadantii Ech703 (DDA), and Rahnella sp. Y9602 (RAH). Conserved cysteine residues are marked in bold blue letters. Asterisks indicate amino acids that are conserved in all listed species. Twin dots and single dots indicate conservative and semiconservative substitutions, respectively. B. β-galactosidase activity from a cpxP-lac transcriptional fusion in the wild-type (AK1052), ΔtrxA mutant (AK1080), ΔtrxB mutant (AK1081), and ΔtrxC mutant (AK1082) strains harboring plasmids pASK or pASK-cacA. Bacteria were grown for 2 h in LB in the presence of 0.2 μg/ml ATc before β-galactosidase activity was measured (arbitrary units) as described . The data correspond to the means of three independent experiments performed in duplicate, and the error bars represent standard deviations.