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Proteins eRF1 and eRF3 are key components of translation termination in eukaryotes. The highly conserved translation termination factor eRF1 decodes stop codons, while another eukaryotic release factor (RF) eRF3 stimulates eRF1 in GTP-dependent manner. Functional C-terminal domain of eRF3 is necessary for cell viability and reveals high degree of similarity between all known eRF3 and elongation factor eEF1A. Unlike the C-terminal part, the N-terminal region of eRF3 proteins is not conserved and contains ‘prion forming domain' (PFD). In mammals, eRF3 homologous proteins can be divided into two subfamilies based on the sequence of their N termini, GSPT1 (eRF3a) and GSPT2 (eRF3b). In our work we hypothesize that GSPT2 gene originated through retrotransposition of processed GSPT1 transcript after divergence between placental and marsupial mammals. Data obtained on the order Rodentia indicate that nucleotide sequence encoding N-terminal part of GSPT2 maybe used as a new marker for philogenetic analysis to distinguish between families. [ABSTRACT FROM AUTHOR]