The dual luciferase reporter plasmids pYDL-control, pYDL-LA, pYDL-Ty1, pYDL-UAA (20) and pYDL-AGC 218 (24) were employed to quantitatively monitor programmed À1 ribosomal frameshifting, programmed +1 ribosomal frameshifting, suppression of a UAA codon and suppression of an AGC serine codon in place of an AGA argine codon in the firefly luciferase catalytic site respectively. In this study, the reporters were housed in LEU2-based reporters: the 0 frame dual luciferase reporter was pJD419, the L-A dsRNA virus À1 PRF containing reporter was pJD420 and the Ty1 containing +1 PRF reporter was pJD421. Cells were grown overnight in 5-ml volumes of -leu synthetic depletion media to mid log phase (A 595 = 0.8-1.5). Cells were washed, resuspended in lysis buffer (1X PBS pH 7.4, 1 mM PMSF) and lysed using 0.5-mm glass beads with a vortex mixer for 3-5 min at 4 C. Lysates were clarified by centrifugation for 5 min. at 8000 r.p.m. at 4 C. Samples were maintained on ice, and 5 ml of clarified lysate was added to 50 ml of pre-aliquoted Promega LARII reagent, mixed by pipetting, and read in a TD20/20 luminometer. Immediately upon completion of this read, 50 ml of Promega Stop and Glo buffer was added to the tube, pipetted to mix and read again. This was repeated 6-12 times per strain per reporter depending on the consistency of the data. Frameshifting rates were determined by taking the ratio of firefly to Renilla luciferases for each sample, and then taking the ratio of the average ratios of the 0 frame samples to that of test reporter ratios to obtain the rates for both À1 and+1 PRF. These results were then analyzed by t-test to determine statistical significance compared to wild-type levels as previously described (25) . Prior to determining rates of UAA readthrough (nonsense suppression), strains were cured of the endogenous yeast prion [PSI + ] by daily serial passage of cells in -trp liquid media containing 5 mM guanidine hydrochloride for 10 days. Rates of nonsense suppression were determined as previously described (20) using the LEU2selectable 0-frame control pJD419 and in-frame UAA containing reporter pJD702. Missense reporters were based on URA3 plasmids previously described for the sense reporter (20) and for the firefly luciferase 218 arginine codon (AGA) to serine (AGC) missense reporter plasmid pYDL-AGC (24) . Methodologies were the same as those for other dual luciferase assays described above.