Figure 4.

Stop codon readthrough can prevent NMD.Top, factors that promote stop codon readthrough: (1) the stop codon triplet used, where the UGA codon is the most permissive stop codon, (2) the identity of the nucleotide at +4 position where stop codon readthrough is promoted the most by a C, and (3) an AU-rich region downstream of the stop codon. Bottom, factors that inhibit stop codon readthrough: These are typically found adjacent to the normal termination codons and include a GC-rich region immediately downstream of the stop codon and the presence of poly-A binding protein 1 (PABP1) in spatial proximity of the termination codon. NMD, nonsense-mediated mRNA decay.