EXPRESSION OF A BUTYRIVIBRIO-FIBRISOLVENS E14 GENE (CINB) ENCODING ANENZYME WITH CINNAMOYL ESTER HYDROLASE ACTIVITY IS NEGATIVELY REGULATED BY THE PRODUCT OF AN ADJACENT GENE (CINR)

A second cinnamoyl ester hydrolase (CEH) encoding gene (cinB) has been characterized from the ruminal bacterium Butyrivibrio fibrisolvens E1 4. CinB is more similar to CinA (previously named CinI) (28% amino aci d identity), the first CEH described from B. fibrisolvens E14, than ei ther of the enzymes are to any other member of the family of hydrolase s to which they belong. Upstream of cinB, and in the opposite orientat ion, is a gene (cinR) encoding a protein with substantial similarity t o members of the MarR family of negative regulators of bacterial gene expression. By alignment of these sequences, a possible helix-turn-hel ix DNA-binding domain has been identified. CinR was expressed at a hig h level in Escherichia coil using the lac promoter. In E. coli CinR re pressed the expression of CinB, but had no effect on the expression of CinA. In gel mobility-shift assays, CinR bound specifically to the ci nR-cinB intergenic region. Two identical 16 nucleotide inverted repeat s adjacent to the putative PcinR and PcinB promoters are likely bindin g sites for CinR. The addition of FAXX (1,3)-O-beta-D-xylopyranosyl-(1 ,4)-D-xylopyranose) and Fara [5-O-(trans-feruloyl)arabinofuranose], bu t not xylobiose, ferulic acid and a number of other soluble components of hemicellulose, inhibited the binding of CinR to DNA.