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

• Site-directed mutagenesis studies established that translation of the tnaC coding region was essential for induction [14].

References