Figure 1. The required programmed +1 frameshifting in decoding the Escherichia coli gene for polypeptide chain release factor 2. The availability of release factor 2 governs the efficiency with which CUU decoding tRNA^Leu shifts from pairing with CUU to the overlapping +1 frame UUU to permit synthesis of more release factor 2. Pairing of the anti-Shine–Dalgarno sequence near the 3¢ end of 16S ribosomal RNA of translating ribosome with a complementary sequence just before the shift site is important for efficient frameshifting.

Figure 2. The programmed –1 frameshifting in decoding Escherichia coli dnaX resulting in the synthesis of two subunits of DNA polymerase III. Tandem slippage at the A6G heptamer is stimulated by the 5¢ ribosomal RNA:messenger RNA interaction and 3¢ stem–loop shown. The ribosomes that shift frame decode one amino acid from the –1 frame, denoted by the orange colour at the C-terminus of the product, before terminating translation at the UGA stop codon marked in red.

Figure 3. Programmed frameshifting in decoding human antizyme 1 as a sensor of cellular polyamine levels for an autoregulatory circuit. A 5¢ element (green), a stop codon (UGA in red) and a 3¢ pseudoknot stimulate frameshifting at the UCC U shift site in a polyamine-dependent manner. Ribosomes that do not frameshift terminate at the UGA stop codon, marked red, to synthesize only the product of the zero frame, marked blue.

Figure 4. Rescue of a ribosome stuck at the end of a broken or incomplete messenger RNA (mRNA) by its transfer to an internal coding sequence of transfer messenger RNA (tmRNA). After resuming protein synthesis by translation of tmRNA, the ribosome quickly encounters a stop codon which causes termination of protein synthesis. It permits dissociation of the ribosome from mRNA and so future use of its component subunits.