Effect of premature termination of translation on mRNA stability depends on the site of ribosome release.

Translational stop codons were introduced at various locations in the protein-coding regions of the monocistronic bla and ompA gene transcripts of Escherichia coli, and the decay characteristics of the upstream and downstream mRNA segments were analyzed. Premature termination of translation at codon position 26 reduced the stability of both the translated and ribosome-free segments of bla mRNA, whereas release of ribosomes just 30 codons further downstream resulted in normal stability for both segments. Normal stability of an untranslated bla gene mRNA segment required its linkage to a ribosome-bound segment of bla gene mRNA. These findings indicate that depriving an mRNA segment of ribosomes does not necessarily render it more susceptible to degradation. However, premature termination of translation at a location that allows ribosomes to traverse only a short segment of bla mRNA can lead to destabilization of the entire transcript.