The Eukaryotic Polypeptide Chain Releasing Factor (eRF3/GSPT) Carrying the Translation Termination Signal to the 3′-Poly(A) Tail of mRNA

Abstract

The mammalian GTP-binding protein GSPT, whose carboxyl-terminal sequence is homologous to the eukaryotic elongation factor EF1␣, binds to the polypeptide chain releasing factor eRF1 to function as eRF3 in the translation termination. The amino-terminal domain of GSPT was, however, not required for the binding. Search for other GSPT-binding proteins in yeast two-hybrid screening system resulted in the identification of a cDNA encoding polyadenylate-binding protein (PABP), whose amino terminus is associating with the poly(A) tail of mRNAs presumably for their stabilization. The interaction appeared to be mediated through the carboxyl-terminal domain of PABP and the aminoterminal region of GSPT. Interestingly, multimerization of PABP with poly(A), which is ascribed to the action of its carboxyl-terminal domain, was completely inhibited by the interaction with the amino-terminal domain of GSPT. These results indicate that GSPT/eRF3 may play important roles not only in the termination of protein synthesis but also in the regulation of mRNA stability. Thus, the present study is the first report showing that GSPT/eRF3 carries the translation termination signal to 3-poly(A) tail ubiquitously present in eukaryotic mRNAs.The yeast GSPT gene, whose product is a GTP-binding protein structurally related to the translation elongation factor EF1␣, was first isolated based on the ability to complement a temperature-sensitive gst1 mutation of Saccharomyces cerevisiae (1). Because DNA synthesis was substantially arrested at the nonpermissive temperature in this mutant, the GSPT gene product appears to play an essential role at the G 1 to S phase transition in the yeast cell cycle. On the other hand, SUP35 was cloned by another group investigating omnipotent suppressor mutant of S. cerevisiae, and the gene turned out to be identical to GSPT (2). Omnipotent suppressor is a class of nonsense suppressors that is recessive and effective toward three types of nonsense codons (3). Mutations in the GSPT/ SUP35 gene were shown to increase the level of translational ambiguity (4, 5), suggesting that this gene product may also function as a positive regulator of translational accuracy in yeast.In eukaryotic protein synthesis, all three types of termination codons are directly recognized by a polypeptide chain releasing factor, eRF1, to release synthesized polypeptide chain from ribosome, and another releasing factor, eRF3, appears to be essentially required for the ribosomal binding of eRF1. Recently, it was reported in S. cerevisiae (6) and Xenopus laevis (7) that the product of the GSPT/SUP35 gene forms a complex with eRF1 to function as eRF3. We previously cloned a human homologue of the yeast GSPT gene (8) and more recently isolated two mouse GSPT genes, the counterpart of human GSPT1 and a novel member of the GSPT gene family, GSPT2 (9). The mammalian GSPT1 and GSPT2 could also associate with eRF1 to function as eRF3, although the two GSPTs were clearly distinct from each other in terms of their amino-terminal sequences, the expression...

Prion-Forming Ability of Ure2 of Yeasts Is Not Evolutionarily Conserved

“…The Sup35p prion domain is important for the normal process of mRNA turnover in yeast and humans (Hoshino et al 1999;Hosoda et al 2003;Funakoshi et al 2007), while the Ure2p prion domain is important for the stability against degradation of the full-length protein (Shewmaker et al 2007). It is likely that these important functions are the basis for the conservation of sequence of these prion domains.…”

Structure and function of the C-terminal PABC domain of human poly(A)-binding protein

“…PABP acts as a general scaffolding protein that recruits various translation factors to the translating mRNA. In addition to the eIF4G subunit of eIF4F, protein partners of PABP include PABP-interacting proteins Paip1 and Paip2, and eukaryotic release factor eRF3 (3)(4)(5). In plants and yeast, additional partners have been identified as follows: eIF4B, Pbp1p, and Rna15p (6)(7)(8).…”

The DAZL and PABP families: RNA-binding proteins with interrelated roles in translational control in oocytes

“…PABP1 can also enhance later steps in translation including 60S subunit joining (Sachs & Davis 1989, Kahvejian et al 2005 and translation termination. PABP1 regulates termination via an interaction with the eukaryotic translation termination factor 3 (eRF3; Hoshino et al 1999) and recent work in yeast described a potential role for the PAB-1-eRF3 interaction in 40S recruitment; but existence of this mechanism has not been described in vertebrates (Amrani et al 2008). The basis for the PABP1-mediated regulation of 60S joining remains enigmatic (Kahvejian et al 2005).…”

“…The mapped region of interaction is depicted by a horizontal line. References: PAIP1 (Craig et al 1998, Gray et al 2000, Roy et al 2002, eIF4G (Imataka et al 1998), PABP1 (Melo et al 2003), DAZL (Collier et al 2005), eRF3 (Hoshino et al 1999). Other experimentally determined protein interactions are not shown including eIF4B.…”