1c). PCR-amplified products of the expected sizes were detected for the internal region of ferB and the intergenic region between ferB and ferA; however, no products for ferC–ferB and ferA-SLG_25010 intergenic regions were obtained. These results suggested that ferB and ferA are organized in the same transcriptional unit. qRT-PCR analyses were performed
to determine the transcriptional regulation of the ferBA operon. As shown in Fig. 2a, the transcription of ferB BAY 57-1293 research buy was induced 6.5-fold in the SYK-6 cells grown on ferulate. However, no induction was observed in the cells grown in the presence of the metabolites of ferulate, vanillin or vanillate, suggesting that the inducer molecule of the ferBA operon is ferulate or its first metabolite, feruloyl-CoA (Fig. 2b). To examine the role of ferC in the transcriptional regulation of the ferBA operon, ferC mutant (SME043) Selleck Navitoclax was created. qRT-PCR analyses showed that ferB was constitutively expressed at a high level in the SME043 cells, indicating that the ferBA operon is negatively regulated by the ferC gene product (Fig. 2a). The ferA mutant (FAK), which is unable to transform ferulate, and the ferB mutant (FBK), which is scarcely able to transform feruloyl-CoA were employed for the qRT-PCR analysis
to determine the inducer of the ferBA operon. SYK-6 has two feruloyl-CoA hydratase/lyase genes, ferB and ferB2 (Masai et al., 2002), but the level of ferB2 transcription was < 10% of that of ferB (data not shown). In the FAK cells, the transcriptional induction of ferB was not observed in the presence of ferulate (Fig. 2b). On the other hand, the Org 27569 transcription of ferB was significantly induced in the FBK cells when ferulate was supplemented (Fig. 2b).
These results indicated that feruloyl-CoA is the actual inducer of the ferBA operon. This fact corresponded to the observation that CoA-thioester intermediates act as inducers for the regulation by FerR, HcaR, and BadR (Egland & Harwood, 1999; Parke & Ornston, 2003; Calisti et al., 2008). To determine the promoter region of the ferBA operon, a DNA fragment containing ferC and the ferC-ferB intergenic region was cloned into a promoter-probe vector pPR9TZ (Kamimura et al., 2010), generating a transcriptional fusion to the promoterless lacZ reporter gene (pPR85). The levels of expression of the lacZ fusion in SME043 cells harboring pPR85 were examined. The β-galactosidase activity was increased 16-fold in the cells grown in the presence of ferulate (Fig. S1). Therefore, the cis-acting region necessary for the transcriptional regulation in response to an inducer seemed to be in the ferC–ferB intergenic region. On the other hand, SME043 cells harboring pPR05, which contains the ferC–ferB intergenic region but not ferC, showed constitutive expression (Fig.