Expression of the release factor eRF1 (Sup45p) gene of higher eukaryotes in yeast and mammalian tissues

Polypeptide chain termination in eukaryotic cells is mediated in part by the release factor eRF1 (Sup45p). We have isolated and characterised cDNAs encoding this translation factor from Syrian hamster (Mesocricetus auratus) and human (Homo sapiens) Daudi cells. Comparison of the deduced amino acid sequence of these new eRF1 (Sup45p) sequences with those published for Saccharomyces cerevisiae, Arabidopsis thaliana, Xenopus laevis and human indicates a high degree of amino acid identity across a broad evolutionary range of species. Both the 5' and 3' UTRs of the mammalian eRF1 (Sup45p)-encoding cDNAs show an unusually high degree of conservation for non-coding regions. In addition, the presence of two different lengths of 3' UTR sequences in the mammalian eRF1 (Sup45p) cDNAs indicated that alternative polyadenylation sites might be used in vivo. Northern blot analysis demonstrated that eRF1 (Sup45p) transcripts of differing length, consistent with the use of alternative polyadenylation sites, were detectable in a wide range of mammalian tissues. The Xenopus, human and Syrian hamster eRF1 (Sup45p) cDNAs were shown to support the viability of a strain of S cerevisiae carrying an otherwise lethal sup45::HIS3 gene disruption indicating evolutionary conservation of function. However, the yeast strains expressing the heterogenous eRF1 (Sup45p) showed a defect in translation termination as defined by an enhancement of nonsense suppressor tRNA activity in vivo. Western blot analysis confirmed that Xenopus eRF1 (Sup45p) was primarily ribosome-associated when expressed in yeast indicating that the ribosome-binding domain of eRF1 (Sup45p) is also conserved.