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Gene Review

tnaC  -  tryptophanase leader peptide

Escherichia coli str. K-12 substr. MG1655

Synonyms: ECK3700, JW3685, tnaL
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Disease relevance of tnaC

  • A short open reading frame consisting of 31 amino acid residues was found upstream of tnaA, and it showed some similarity to the E. coli tnaC gene known to be a cis-acting regulatory element for transcription [1].
  • Roles of the tnaC-tnaA spacer region and Rho factor in regulating expression of the tryptophanase operon of Proteus vulgaris [2].

High impact information on tnaC

  • The 24 residue leader peptidyl-tRNA of the tna operon of E. coli, TnaC-tRNA(Pro), in the presence of excess tryptophan, resists cleavage at the tnaC stop codon [3].
  • Tryptophan acts by inhibiting Release Factor 2-mediated cleavage of this peptidyl-tRNA at the tnaC stop codon [4].
  • Using a minimal in vitro transcription system consisting of a tna template, RNA polymerase, and Rho, it was shown that RNA sequences immediately adjacent to the tnaC stop codon, the presumed boxA and rut sites, contributed most significantly to Rho-dependent termination [5].
  • The ribosome associated with this newly synthesized peptidyl-tRNA presumably stalls at the tnaC stop codon, blocking Rho's access to the BoxA and rut sites, thereby preventing termination [6].
  • These findings establish that the growth inhibition caused by tnaC overexpression during induction by tryptophan is primarily a consequence of tRNA(Pro) depletion, resulting from TnaC-tRNA(Pro) retention within stalled, translating ribosomes [7].

Biological context of tnaC

  • Translation of the single Trp codon in tnaC of the multicopy plasmids was shown to be essential for this inhibition [8].
  • Plasmid-mediated overexpression of tnaC, under inducing conditions, reduced cell growth rate appreciably [7].
  • Stop codons introduced downstream of Trp codon 12 in all three reading frames established that induction requires translation in the natural tnaC reading frame [9].

Associations of tnaC with chemical compounds

  • Inhibition by tryptophan is not observed when Trp codon 12 of tnaC is changed to a Leu codon [10].
  • Deletions that removed 28 to 30 bp from the region immediately following tnaC increased basal-level expression about threefold and allowed threefold induction by 1-methyltryptophan [2].
  • The last sense codon of tnaC, proline codon 24 (CCU), is translated by tRNA(2)(Pro) [7].
  • At the tna promoter, urea does not abolish transcription initiation but could interfere with tnaC translation [11].
  • The tnaC leader portion of the tnaA promoter was found to reduce pre-induction expression in the presence of glucose, although maximal expression was observed only in the absence of this region [12].

Other interactions of tnaC

  • Our results suggest that translation of tnaC is essential for the prfC effect [13].

Analytical, diagnostic and therapeutic context of tnaC


  1. Cloning and characterization of a tryptophanase gene from Enterobacter aerogenes SM-18. Kawasaki, K., Yokota, A., Oita, S., Kobayashi, C., Yoshikawa, S., Kawamoto, S., Takao, S., Tomita, F. J. Gen. Microbiol. (1993) [Pubmed]
  2. Roles of the tnaC-tnaA spacer region and Rho factor in regulating expression of the tryptophanase operon of Proteus vulgaris. Kamath, A.V., Yanofsky, C. J. Bacteriol. (1997) [Pubmed]
  3. Features of ribosome-peptidyl-tRNA interactions essential for tryptophan induction of tna operon expression. Cruz-Vera, L.R., Rajagopal, S., Squires, C., Yanofsky, C. Mol. Cell (2005) [Pubmed]
  4. Changes produced by bound tryptophan in the ribosome peptidyl transferase center in response to TnaC, a nascent leader peptide. Cruz-Vera, L.R., Gong, M., Yanofsky, C. Proc. Natl. Acad. Sci. U.S.A. (2006) [Pubmed]
  5. Analysis of tryptophanase operon expression in vitro: accumulation of TnaC-peptidyl-tRNA in a release factor 2-depleted S-30 extract prevents Rho factor action, simulating induction. Gong, F., Yanofsky, C. J. Biol. Chem. (2002) [Pubmed]
  6. Reproducing tna operon regulation in vitro in an S-30 system. Tryptophan induction inhibits cleavage of TnaC peptidyl-tRNA. Gong, F., Yanofsky, C. J. Biol. Chem. (2001) [Pubmed]
  7. Overexpression of tnaC of Escherichia coli inhibits growth by depleting tRNA2Pro availability. Gong, M., Gong, F., Yanofsky, C. J. Bacteriol. (2006) [Pubmed]
  8. Inhibition of expression of the tryptophanase operon in Escherichia coli by extrachromosomal copies of the tna leader region. Gish, K., Yanofsky, C. J. Bacteriol. (1993) [Pubmed]
  9. Evidence suggesting cis action by the TnaC leader peptide in regulating transcription attenuation in the tryptophanase operon of Escherichia coli. Gish, K., Yanofsky, C. J. Bacteriol. (1995) [Pubmed]
  10. Regulation of the Escherichia coli tna operon: nascent leader peptide control at the tnaC stop codon. Konan, K.V., Yanofsky, C. J. Bacteriol. (1997) [Pubmed]
  11. Two different mechanisms for urea action at the LAC and TNA operons in Escherichia coli. Blazy, B., Ullmann, A. Mol. Gen. Genet. (1990) [Pubmed]
  12. Use of a modified tryptophanase promoter to direct high-level expression of foreign proteins in E. coli. Sitney, K.C., Mann, M.B., Stearns, G.W., Menjares, A.D., Stevenson, J.L., Snavely, M.D., Fieschko, J.C., Curless, C., Tsai, L.B. Ann. N. Y. Acad. Sci. (1996) [Pubmed]
  13. Loss of overproduction of polypeptide release factor 3 influences expression of the tryptophanase operon of Escherichia coli. Yanofsky, C., Horn, V., Nakamura, Y. J. Bacteriol. (1996) [Pubmed]
  14. 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. Kamath, A.V., Yanofsky, C. J. Biol. Chem. (1992) [Pubmed]
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