Evolution of translation termination factor eRF3: Is GSPT2 generated by retrotransposition of GSPT1's mRNA?

Two release factors (eRF1 and eRF3) are responsible for correct termination of translation in eukaryotes. While the structure and functions of different domains of eRF1 have been sufficiently characterized, the role of eRF3 in translation termination remains unclear. Moreover, the N-terminal domain of eRF3, which is dispensable for termination, is highly divergent. Mammalian eRF3 exists in two isotypes, eRF3a and eRF3b, encoded by genes GSPT1 and GSPT2, respectively. Here we propose that GSPT2 originated through retrotransposition of processed GSPT1 transcript into the genome. Comparison of the 5' non-coding sequences of both genes revealed existence of potential promoter element in 5' UTR of GSPT1 which we suppose to be responsible for GSPT2 transcription.