Role of the TnaC peptide residues in the regulation of the ribosome function by L-Trp in E. coli.

摘要

The tnaCAB operon in E. coli is involved in the catabolism of L-tryptophan. High concentrations of L-Trp induce the expression of the tnaA and tnaB structural genes, whose products are the Tryptophanase enzyme and a L-Trp Permease. The nascent TnaC peptide product of this operon induces the L-Trp dependent ribosome stalling and regulates the expression of structural genes. We observed that changes of the TnaC Lys 18 residue by a small, bulky or opposite charge residue do not affect the L-Trp dependent ribosome stalling. However, similar changes on the TnaC I1e19 residue eliminate the inhibition by L-Trp. Interestingly, the I1e19 residue replacements by hydrophobic residues such as Leu, Met or Val have little or no effect on the inhibition by L-Trp. Furthermore, replacement of the TnaC Va120 residue by bulky residue eliminates the inhibition by L-Trp. Our results propose that TnaC I1e19 and Va120 residues are involved in interacting with ribosome components or with L-Trp to induce ribosome stalling.