Quantitative northern blot analysis was used to examine whether the observed translation products ending within the pseudoknot structure arose from fragments of mRNA produced either by low RNA-polymerase processivity or specific endonucleolytic attacks by RNases at the pseudoknot sequences. No evidence was found of a specific population of transcripts that could explain the amounts of protein products attributed to originate from pseudoknot-stalled ribosomes. Also, our protein-stability assay showed that the translational products from the stalled ribosomes were stable for at least 80 min (Supplementary Figure S1) , thus indicating that the stalled ribosomes are not rescued by tmRNA and that the stalled proteins do not originate from truncated mRNA.