Figure 2. Mechanisms of PTC recognition.

Figure 2

Mechanisms of PTC recognition. A premature termination codon (PTC) is recognized relative to the position of a downstream cis-acting signal that varies across species. In mammals (A), the cis-acting signal is an exon-exon junction marked by a group of proteins that constitute the exon junction complex (EJC). In yeast and fruitfly (B), the cis-acting signal is a faux 3'-UTR. Natural termination codons (STOP), in contrast to PTCs, are flanked by proper 3'-untranslated region (UTR) marked by a specific protein or set of proteins, including the poly(A)-binding protein shown over the poly(A) tail.

From: NMD in Drosophila: A Snapshot into the Evolution of a Conserved mRNA Surveillance Pathway

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