Abstract
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.
Highlights
CLONING, NUCLEOTIDESEQUENCE, AMINO ACID HOMOLOGY, AND IN VITRO SYNTHESIS OF THE LEADER PEPTIDE AND REGULATORY ANALYSIS*
Both operons contain two major structural genes, tnaA studied most extensively [1,6, 7]; its amino acid sequence has and tnaB,that encode tryptophanase and a tryptophan been determined both by protein sequencing [8] and by depermease, respectively. tnaA of P. vulgaris is preceded duction from the nucleotide sequence of its encoding strucby a transcribed leader region, encoding a 34-residue leader peptide, TnaC, that contains a single tryptophan residue
Regulatory studies performed in P. vulgaris, and witha plasmid carrying the P. vulgaris tnaoperon in E. coli, established that expression of the Proteus operon was induced by tryptophan and was subject to catabolite repression
Summary
CLONING, NUCLEOTIDESEQUENCE, AMINO ACID HOMOLOGY, AND IN VITRO SYNTHESIS OF THE LEADER PEPTIDE AND REGULATORY ANALYSIS*. Vulgaris leader peptide was demonstratedin an in vitro The tna operon of E. coli contains two major structural coupled transcription-translation system. Tryptophanase (Tnase) catalyzes the Translation of the tnaC coding regionis required for this synthesis of tryptophan from indole and serine or cysteine tryptophan-induced transcription antiterminationin the tna [1,2,3]. The leader peptide coding including Escherichia coli [3], Bacillus alvei [4],and Proteus region contains asingle tryptophan codon at position 12which rettgeri ( 5 ) .Tnases isolated from these sources have a similar must be translated by tRNATv for induction to occur [18]. How inducing levels of tryptophan aresensed in the induction process, and how this sensing leads to transcription antitermination, are not known
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