Fig. 3. Balon resembles and probably shares its origin with the archaeo-eukaryotic proteins aeRF1 and Pelota.

a, Comparison illustrating structural similarity between Balon, aeRF1 and Pelota proteins. The overall structure of Balon most closely resembles that of the translation termination factor aeRF1: it shares a common domain organization and binds the ribosome in a similar way through contacts with EF-Tu, the decoding centre and the peptidyl-transferase centre. Balon lacks key structural features that are required for aeRF1 activity, including the NIKS motif (stop-codon recognition) and the GGQ motif (nascent peptide release). b, Zoomed-in views of the cryo-EM map and the ribosome structure (in state 2) highlighting the molecular contacts between key structural features of Balon and the active centres of the ribosome or EF-Tu.