Ribosome–mRNA complex at premature UGA stop codons (PTC-ribosome complex (UGA))

The ribosome–mRNA complex at premature UGA stop codons is a specialized state of the translational machinery where protein synthesis is prematurely halted due to a nonsense mutation. In this complex, the ribosome encounters a UGA (opal) stop codon in the middle of an open reading frame, leading to the recruitment of release factors and the production of truncated, often deleterious, proteins (Mort et al., 2008, Human Mutation 29(8):1037-49). This target is the focus of nonsense suppression therapy, where pharmacological agents like ataluren or aminoglycosides interact with the ribosomal A-site to decrease the stringency of codon-anticodon pairing (Welch et al., 2007, Nature 447(7140):87-91). By facilitating the incorporation of a near-cognate aminoacyl-tRNA instead of a release factor, these drugs allow the ribosome to bypass the premature UGA codon and continue translating until the natural stop codon is reached. This restoration of full-length protein production offers a potential treatment for a wide array of genetic diseases, including Duchenne muscular dystrophy and cystic fibrosis, which are frequently caused by such mutations (Linde & Kerem, 2008, Trends in Genetics 24(11):552-63). However, therapeutic success depends on the specific nucleotide context surrounding the UGA codon and the ability to avoid interfering with normal termination at the ends of genes (Peltz et al., 2013, FEBS Letters 587(11):1605-12). The complex also plays a role in triggering nonsense-mediated mRNA decay (NMD), a surveillance pathway that degrades mRNAs containing PTCs to prevent the accumulation of truncated proteins. Targeting this complex effectively requires balancing the promotion of read-through at the PTC while maintaining the fidelity of translation at legitimate stop codons to minimize systemic toxicity.

Other names

Premature termination codon complexNonsense mutation-stalled ribosomeUGA-stalled translation complexRibosomal decoding center at PTC

Induction of translational read-through by binding to the ribosomal decoding center and promoting the insertion of near-cognate aminoacyl-tRNA at premature stop codons.