Figure 3

The cacA promoter harbors a conserved -10 region sequence that is crucial for RpoS-dependent regulation. A. Alignment of the DNA sequences of the intergenic region between the cacA-coding region and its upstream ORF (STM1851) in E. coli (ECO), C. koseri (CKO), Enterobacter sp. 638 (ENT), S. enterica serovar Typhimurium LT2 (STM), Klebsiella pneumoniae (KPN), and C. sakazakii (ESA). Asterisks correspond to nucleotides that are conserved in all listed species. Twin dots and single dots indicate conservative and semiconservative substitutions, respectively. The -10 region sequence is marked in bold blue letters. The bent arrow indicates the transcription start site (TSS) of the cacA transcript, as determined by a recent report [30] (designated position +1). The inverted arrows indicate predicted Rho-independent terminator sequences. The initiation codons for the cacA gene are boxed. B. Designated mutations in the cacA promoter. The -10 region sequence (CTA cac T from -13 to -7) [29] represents a consensus sequence that is recognized by RpoS. The -10 region sequence of the cacA promoter is highlighted in blue. The numbers shown above the wild-type sequence are the positions relative to the cacA TSS [30]. The substituted nucleotides (-14C/G, -16T/A -14C/G, and -12A/T -8T/A) are underlined. C. β-galactosidase activity from a P _cacA -lac transcriptional fusion 2 in the wild-type (−; AK1067), ΔrpoS mutant (AK1071), -14C/G cacA promoter mutant (AK1068), ΔrpoS -14C/G cacA promoter mutant (AK1072), -16T/A -14C/G cacA promoter mutant (AK1069), ΔrpoS -16T/A-14C/G cacA promoter mutant (AK1073), -12A/T -8T/A cacA promoter mutant (AK1070), and ΔrpoS -12A/T -8T/A cacA promoter mutant (AK1074) strains. Bacteria were grown for 4 h in LB before β-galactosidase activity was measured (arbitrary units) as described [42]. The data correspond to the means of three independent experiments performed in duplicate, and the error bars represent standard deviations.