Reactions contained 4 ml of RNA solution, 4.5 ml of reticulocyte lysate (Promega), 1 ml of 35 S methionine (ICN, in vitro translation grade), 0.5 ml of 1 mM amino acids (ÀMet) and were incubated for 60 min at 28 C. Samples were boiled for 3 min in the Laemmli buffer and loaded onto 12% SDS polyacrylamide gels. Gels were dried and exposed to phosphoimager screens. Band intensity of 0 frame and À1 frame products was measured using Molecular Imager FX (Biorad) and Quantity One software. Frameshift percentages were calculated as the amount of À1 frame product divided by the sum of 0 and À1 frame products, corrected for the number of methionines, multiplied by 100.