Characterization of the tryptophanase operon of Proteus vulgaris. Cloning, nucleotide sequence, amino acid homology, and in vitro synthesis of the leader peptide and regulatory analysis

The tryptophanase (tna) operon of Proteus vulgaris was cloned and characterized and found to be organized similarly to the tna operon of Escherichia coli. Both operons contain two major structural genes, tnaA and tnaB, that encode tryptophanase and a tryptophan permease, respectively. tnaA of P. vulgaris is preceded by a transcribed leader region, encoding a 34-residue leader peptide, TnaC, that contains a single tryptophan residue. The tnaC coding region also has a boxA-like sequence. Regulatory studies performed in P. vulgaris, and with a plasmid carrying the P. vulgaris tna operon in E. coli, established that expression of the Proteus operon was induced by tryptophan and was subject to catabolite repression. Site-directed mutagenesis studies established that translation of the tnaC coding region was essential for induction. Synthesis of the P. vulgaris leader peptide was demonstrated in an in vitro coupled transcription-translation system. Interestingly, the 5 amino acid residues of the TnaC peptide surrounding the sole tryptophan residue are identical in P. vulgaris and E. coli. We conclude that the tna operon of P. vulgaris is also regulated by tryptophan-induced transcription antitermination. Homology of tryptophanase and tryptophan permease of P. vulgaris to related proteins from other species is described.