Inhibition of expression of the tryptophanase operon in Escherichia coli by extrachromosomal copies of the tna leader region.
Expression of the tryptophanase (tna) operon in Escherichia coli is regulated by catabolite repression and transcription attenuation. Expression is induced by the presence of elevated levels of tryptophan in a growth medium devoid of a catabolite-repressing carbon source. Induction requires the translation of a 24-residue coding region, tnaC, located in the 319-nucleotide transcribed leader region preceding tnaA, the structural gene for tryptophanase. Multicopy plasmids carrying the tnaC leader region were found to inhibit induction of the chromosomal tna operon. Mutational studies established that this inhibition was not due to inhibited transcription initiation, translation initiation, tryptophan transport, or enzyme activity. Rather, multicopy tnaC plasmids inhibited induction by preventing tryptophan-induced transcription antitermination in the leader region of the tna operon. Translation of the single Trp codon in tnaC of the multicopy plasmids was shown to be essential for this inhibition. We hypothesize that translation of the Trp codon of the leader peptide titrates out a trans-acting factor that is essential for tryptophan-induced antitermination in the chromosomal tna operon. We postulate that this factor is an altered form of tRNATrp.
Department of Biological Sciences, Stanford University, California 94305-5020.
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Yanofsky
D000483:Alleles; D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics; D003001:Cloning, Molecular; D004790:Enzyme Induction; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D029968:Escherichia coli Proteins; D005111:Extrachromosomal Inheritance; D015964:Gene Expression Regulation, Bacterial; D026901:Membrane Transport Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic; D012364:RNA, Transfer, Trp / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D014368:Tryptophanase / Q000235:genetics*
D026905:Amino Acid Transport Systems; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D012364:RNA, Transfer, Trp; D011993:Recombinant Fusion Proteins; C081473:tnaC protein, E coli; C035131:TnaB protein, E coli; D014368:Tryptophanase