**5. Conclusion**

162 Gene Duplication

eRF1) (Carr-Schmid et al., 2002). Indeed, Hbs1 forms a complex with Dom34 and GTP (Dom34-Hbs1-GTP), similar to that of eRF1-eRF3-GTP (Hauryliuk et al., 2006; Graille et al., 2008; Chen et al., 2010; Shoemaker et al., 2010; van den Elzen et al., 2010). The central event of NGD is mRNA cleavage, and Dom34 has the necessary RNase activity (Lee et al., 2007; Graille et al., 2008), although the proposed endonuclease activity of Dom34 is not required for mRNA cleavage in NGD (Passos et al., 2009). Dom34 of *S. cerevisiae* consists of three domains, two of which are homologous to the corresponding domains in eRF1, while the Nterminal domain of Dom34 is different from that of eRF1 and is probably necessary for the

Fig. 4. Neofunctionalization of termination factors in mRNAs quality control systems. Three systems described for *S. cerevisiae* are shown. NSD (Non-stop decay) is responsible for the degradation of transcripts lacking stop codons. NGD (No-go decay) removes mRNA secondary structures that prevent translation. NMD (Nonsense-mediated decay) destroys

transcripts containing nonsense mutations. See text for details.

Successive duplications of genes encoding elongation factors for translation led to the emergence of several protein complexes with different properties. The eRF1-eRF3 complex terminates translation, and the Dom34-Hbs1 complex is involved in the quality control of mRNA. Both eRF1 and eRF3 interact not only with each other but also with additional proteins. Some of these interactions are possibly mutually exclusive, and some of the proteins interacting with eRF1/eRF3 can be components of the complex terminating translation. Possible candidates for involvement in termination are poly(A) binding protein (PABP) and Upf proteins (Upf1, Upf2 and Upf3). Interaction of eRF3 with PABP links termination of translation with initiation (Hoshino et al., 1999), while interaction with Upf involves eRF proteins in nonsense-mediated decay (Amrani et al., 2006). The genetic data, derived mostly from *S. cerevisiae*, strongly suggest that the functions of eRF1 and eRF3 are not restricted to termination of translation (Inge-Vechtomov et al., 2003). Further studies are needed to characterize other non-translational functions of both proteins, as was shown for eEF1A (Mateyak & Kinzy, 2010).
