confirm this, we searched the promoter sequence of benA using in silico analysis. The nucleotide sequence upstream of the benABCD operon has the following sequence features: a putative -10/-35-type promoter, a putative BenR-binding region, and a predicted translational start site (Figure 6A). Comparison with the experimentally well-characterized Torin 1 BenR-binding sequences in P. putida  indicated a highly conserved BenR site in the promoter region of the A1501 benA gene (Figure 6A). To determine whether benR is required for activation of the PbenA promoter, the expression level of the benABCD operon was tested in the benR mutant A1601. Quantitative real-time PCR results demonstrated that a significant increase in transcription from the PbenApromoter
was seen in wild-type A1501 when benzoate was included in the growth medium, whereas the addition of catechol or cis,cis-muconate had a very weak effect (Figure 6B). When BenR was absent, transcription from the PbenA promoter was highly repressed, irrespective of the presence or absence of the inducer (Figure 6B). As reported in P. putida , these results led us to conclude that the benABCD operon is under the control of BenR LOXO-101 research buy in response to benzoate in A1501. Figure 6 Induction of the benA or catB promoters in culture media with several different inducers. The putative binding site for BenR or CatR is boxed. The putative
-10/-35 promoter consensus sequences are indicated by asterisks. The predicted transcriptional start site (+1) and ribosome-binding site (RBS) are underlined. (A) Nucleotide sequence of the CYTH4 benR-benA intergenic region of strain A1501. (B) Quantitative real-time RT-PCR analysis of relative benA expression level of the wild type (black bars) and benR mutant (gray bars) in the presence or absence of benzoate (BEN), catechol (CAT), cis, cis-muconate (CCM), and lactate (LAC). (C) Comparison of the catB promoter of strain A1501 with those of P. putida PRS2000, P. aeruginosa PAO1 and P. fluorescens pf-5. Dashes indicate gaps to obtain maximal homology. (D) Quantitative real-time RT-PCR analysis of relative catB expression level of the wild type (black bars) and benR mutant (gray bars) in the presence or absence of benzoate (BEN), catechol (CAT), cis, cis-muconate (CCM), and lactate (LAC). Relative levels of transcripts are presented as the mean values ± SD, calculated from three sets of independent experiments. Benzoate-mediated induction of the catBC operon in A1501 In P. putida, the catBC operon encodes cis,cis-muconate lactonizing enzyme I (CatB) and muconolactone isomerase (CatC), which catalyze the second and third steps of the catechol branch of the β-ketoadipate pathway, respectively . The transcription of this operon requires CatR and cis,cis-muconate .