Suppression of premature termination codons as a therapeutic approach.

In this review, we describe our current understanding of translation termination and pharmacological agents that influence the accuracy of this process. A number of drugs have been identified that induce suppression of translation termination at in-frame premature termination codons (PTCs; also known as nonsense mutations) in mammalian cells. We discuss efforts to utilize these drugs to suppress disease-causing PTCs that result in the loss of protein expression and function. In-frame PTCs represent a genotypic subset of mutations that make up ~11% of all known mutations that cause genetic diseases, and millions of patients have diseases attributable to PTCs. Current approaches aimed at reducing the efficiency of translation termination at PTCs (referred to as PTC suppression therapy) have the goal of alleviating the phenotypic consequences of a wide range of genetic diseases. Suppression therapy is currently in clinical trials for treatment of several genetic diseases caused by PTCs, and preliminary results suggest that some patients have shown clinical improvements. While current progress is promising, we discuss various approaches that may further enhance the efficiency of this novel therapeutic approach.

Identification of eRF1 residues that play critical and complementary roles in stop codon recognition.

The initiation and elongation stages of translation are directed by codon-anticodon interactions. In contrast, a release factor protein mediates stop codon recognition prior to polypeptide chain release. Previous studies have identified specific regions of eukaryotic release factor one (eRF1) that are important for decoding each stop codon. The cavity model for eukaryotic stop codon recognition suggests that three binding pockets/cavities located on the surface of eRF1's domain one are key elements in stop codon recognition. Thus, the model predicts that amino acid changes in or near these cavities should influence termination in a stop codon-dependent manner. Previous studies have suggested that the TASNIKS and YCF motifs within eRF1 domain one play important roles in stop codon recognition. These motifs are highly conserved in standard code organisms that use UAA, UAG, and UGA as stop codons, but are more divergent in variant code organisms that have reassigned a subset of stop codons to sense codons. In the current study, we separately introduced TASNIKS and YCF motifs from six variant code organisms into eRF1 of Saccharomyces cerevisiae to determine their effect on stop codon recognition in vivo. We also examined the consequences of additional changes at residues located between the TASNIKS and YCF motifs. Overall, our results indicate that changes near cavities two and three frequently mediated significant effects on stop codon selectivity. In particular, changes in the YCF motif, rather than the TASNIKS motif, correlated most consistently with variant code stop codon selectivity.