Polypeptides originating from stalled ribosomes were found as radioactive polypeptides with appropriate isoelectric point and molecular weight appearing on gels when the translated transcript contained a pseudoknot. These polypeptides were absent when a transcript without a pseudoknot was translated. The weakest stalled protein spots were difficult to distinguish from spots originating from endogenous gene expression on these gels (compare to the 0 construct in Supplementary Figure S5 ) and their determination is connected with some uncertainty. The statistical analysis used to compare the stalling efficiency between pseudoknot 22/6a and 22/6b was an unpaired one-tailed Student's t-test with a significance level of 0.05.