To anneal the oligonucleotides with the mRNA, J-oligos, R-oligos or the equivalent volumes of dilution buffer alone (20 mM Tris, pH 7.4, 2 mM MgCl 2 and 50 mM EDTA final concentration) were added to synthetic mRNA (0.5 mg), and the mixtures were first incubated in a 70 C heating block for 10 min; the block was then removed and allowed to cool to 37 C (30 min), after which they were briefly spun down and incubated on ice. In all experiments, the molar ratios of J-and R-oligos to synthetic mRNAs were 100:1. In experiments using the competing oligonucleotide (C-oligo), this was added to either 0.5:1 or 1:1 molar ratios with either J-or R-oligonucleotides. Reticulocyte lysates were thawed on ice, 15 ml of Àmet and 15 ml of Àleu master mixes plus 20 ml of H 2 O were added to 400 ml of lysate, and 19 ml of this was added to each annealed reaction to start the in vitro translation reactions. These were incubated at 30 C for 60 min (the reaction reached a plateau after 30-35 min where the greatest difference was seen between the zero-frame controls and the frameshifting plasmids) (data not shown), and the reactions were then placed on ice. An aliquot of 7.5 ml from each in vitro translation reaction was added to 50 ml of the prewarmed luciferase reagent, and luminescence readings were taken after a 3 s delay for 15 s in triplicate using a Turner 20/20 Luminometer.