Fig. 13

Decrease in translation termination efficiency by the ψ (PSI) factor. a Translation termination in normal cells. When actively translating 80S ribosomes reach the termination codon on mRNA, eRF instead of aminoacyl-tRNA enters into the A site of ribosomes. Translation then ceases, leading to the dissociation of the nascent polypeptide, tRNA, and eRF from ribosomes. Ribosomes themselves also dissociate to 40S and 60S subunits. b PSI ⁺ generation by the aggregation of Sup35. Since functional Sup35 is depleted, the efficiency of translation termination is decreased, allowing the entry of aminoacyl-tRNA into the ribosome A site. Ribosomes continue to translate the 3′-UTR of mRNA beyond the intrinsic termination codon. This may cause the C-terminal extension of nascent polypeptides, as well as the suppression of natural nonsense mutations