STOP AND GO SIGNALS: Certain ciliates use traditional stop codons ambiguously during translation. Sometimes these three-base-long RNA sequences code for an amino acid (green, left), and sometimes induce translation termination (red, right). Researchers propose that at the end of the mRNA coding sequence, the ribosome bumps up against proteins involved in termination—namely, eukaryotic release factors (eRF1 and eRF3) and poly(A) binding proteins (PABP)—thereby indicating that a stop codon means stop.© KIMBERLY BATTISTA
The paper
E.C. Swart et al., “Genetic codes with no dedicated stop codon: Context-dependent translation termination,” Cell, 166:691-702, 2016.
The genetic code—the digital set of instructions often laid out in tidy textbook tables that tells the ribosome how to build a peptide—is identical in most eukaryotes. But as with most rules, there are exceptions. During a recent project on genome rearrangement in ciliates, Mariusz Nowacki, a cell biologist at the University of Bern in Switzerland, and his team stumbled across two striking deviants.
Ciliates, complex protozoans with two nuclei, are known to translate RNA transcripts in unorthodox ways. Nowacki’s team, however, discovered that Condylostoma magnum and an unclassified Parduczia species had gone even further, reassigning all of the traditional “stop” codons (UGA, UAA, and UAG) ...
