Nucleotide sequence and regulation of a gene involved in bile acid 7-dehydroxylation by Eubacterium sp. strain VPI...

Eubacterium sp. strain VPI 12708 is an anaerobic intestinal bacterium that has inducible bile acid 7-dehydroxylation activity. At least four new polypeptides were synthesized after addition of primary bile acids to the growth medium. One of these, of molecular weight 27,000 (P-27), was shown to be involved in the 7-dehydroxylation reaction sequence. The gene coding for P-27 was cloned, and the entire DNA sequence for the protein-coding region was determined. In addition, sequence information was obtained for 294 bases upstream from the translational start codon and 329 bases downstream from the stop codon. Induction studies with a synthetic oligonucleotide probe (16-mer) revealed the presence of a cholic acid-inducible mRNA species approximately 900 bases long. A 5' terminus of this mRNA was detected by primer extension analysis, and the location of the 3' terminus of the mRNA was estimated by using S1 nuclease mapping. The 3' terminus of the mRNA contained a large element with dyad symmetry of unknown function. The open reading frame contained 249 codons, and the corresponding polypeptide had a calculated molecular weight of 26,745. The amino acid sequence of P-27 showed significant homology to several previously described alcohol-polyol dehydrogenases ("nonzinc" dehydrogenases), especially in the region believed to contain a pyridine nucleotide-binding domain. The implications of this homology and the possible function of P-27 in bile acid 7-dehydroxylation are discussed.