Expression of the Escherichia coli tryptophanase operon depends on ribosome stalling during translation of the upstream TnaC leader peptide, a process for which interactions between the TnaC nascent chain and the ribosomal exit tunnel are critical.
Attempts to decode and translate such «nonstop - mRNAs» leads to a complete stalling of the ribosomal machinery, resulting in effectively blocking continued protein synthesis.