Fig. 2.

Frameshift assay. Autoradiogram of SDS-polyacrylamide gel showing proteins metabolically labeled by [³⁵S]methionine. Expression from plasmids of genes encoding frameshift sites are induced by the presence of IPTG. For the constructs encoding pseudoknots, PK400 or PK401, induction leads to synthesis of two proteins (see arrows): one protein from ribosomes terminated at the zero frame stop codon, which follows the slippery sequence, and another protein from ribosomes which frameshifted to the −1 frame. Only the termination product is detected for the construct with no pseudoknot, PK421. Percent frameshift is given above each lane.