APE-Type Non-LTR Retrotransposons of Multicellular Organisms Encode Virus-Like 2A Oligopeptide Sequences, Which Mediate Translational Recoding during Protein Synthesis

2A oligopeptide sequences (“2As”) mediate a cotranslational recoding event termed “ribosome skipping.” Previously we demonstrated the activity of 2As (and “2A-like sequences”) within a wide range of animal RNA virus genomes and non-long terminal repeat retrotransposons (non-LTRs) in the genomes of the unicellular organisms Trypanosoma brucei (Ingi) and T. cruzi (L1Tc). Here, we report the presence of 2A-like sequences in the genomes of a wide range of multicellular organisms and, as in the trypanosome genomes, within non-LTR retrotransposons (non-LTRs)—clustering in the Rex1, Crack, L2, L2A, and CR1 clades, in addition to Ingi. These 2A-like sequences were tested for translational recoding activity, and highly active sequences were found within the Rex1, L2, CR1, and Ingi clades. The presence of 2A-like sequences within non-LTRs may not only represent a method of controlling protein biogenesis but also shows some correlation with such apurinic/apyrimidinic DNA endonuclease-type non-LTRs encoding one, rather than two, open reading frames (ORFs). Interestingly, such non-LTRs cluster with closely related elements lacking 2A-like recoding elements but retaining ORF1. Taken together, these observations suggest that acquisition of 2A-like translational recoding sequences may have played a role in the evolution of these elements.