Eap1p, a Novel Eukaryotic Translation Initiation Factor 4E-Associated Protein in Saccharomyces cerevisiae

Abstract

Ribosome binding to eukaryotic mRNA is a multistep process which is mediated by the cap structure [m 7 G(5)ppp(5)N, where N is any nucleotide] present at the 5 termini of all cellular (with the exception of organellar) mRNAs. The heterotrimeric complex, eukaryotic initiation factor 4F (eIF4F), interacts directly with the cap structure via the eIF4E subunit and functions to assemble a ribosomal initiation complex on the mRNA. In mammalian cells, eIF4E activity is regulated in part by three related translational repressors (4E-BPs), which bind to eIF4E directly and preclude the assembly of eIF4F. No structural counterpart to 4E-BPs exists in the budding yeast, Saccharomyces cerevisiae. However, a functional homolog (named p20) has been described which blocks cap-dependent translation by a mechanism analogous to that of 4E-BPs. We report here on the characterization of a novel yeast eIF4E-associated protein (Eap1p) which can also regulate translation through binding to eIF4E. Eap1p shares limited homology to p20 in a region which contains the canonical eIF4E-binding motif. Deletion of this domain or point mutation abolishes the interaction of Eap1p with eIF4E. Eap1p competes with eIF4G (the large subunit of the cap-binding complex, eIF4F) and p20 for binding to eIF4E in vivo and inhibits cap-dependent translation in vitro. Targeted disruption of the EAP1 gene results in a temperature-sensitive phenotype and also confers partial resistance to growth inhibition by rapamycin. These data indicate that Eap1p plays a role in cell growth and implicates this protein in the TOR signaling cascade of S. cerevisiae.

The SESA network links duplication of the yeast centrosome with the protein translation machinery

“…Deregulating initiation by overexpression of the CAP-binding protein eIF4E leads to malignant transformation and therefore, not surprisingly, eIF4E is elevated in many human cancers (De Benedetti and Rhoads 1990;Lazaris-Karatzas et al 1990). In addition, TOR signaling and stress situations including membrane defects inhibit global initiation of translation by regulating binding of proteins (4E-BPs) to the initiation factor eIF4E (Cosentino et al 2000;Deloche et al 2004;Matsuo et al 2005;Ibrahimo et al 2006).…”

“…In response to SPB duplication defects, the SESA network, comprising of the known mRNA-binding protein Scp160 (Frey et al 2001;Li et al 2003Li et al , 2004Baum et al 2004), the ribosomeassociated Asc1 (Baum et al 2004;Gerbasi et al 2004), the translation inhibitor Eap1 (Cosentino et al 2000), and the protein Smy2 (Kofler et al 2005), was identified as being responsible for the translation control of POM34 mRNA. We demonstrate that SESA inhibits translation of POM34 mRNA by binding of the 4E-BP Eap1 to the conserved translation initiation factor eIF4E.…”

Mechanism and Regulation of Protein Synthesis in Saccharomyces cerevisiae

“…A central region of eIF4G (eIF4G1 ) binds to eIF4E on the opposite face to the 59 cap interaction ( Figure 6B). The eIF4E-4G binding interface overlaps with the surface important for binding 4E-binding proteins (4E-BPs) Caf20 and Eap1 that inhibit eIF4F assembly by competing with eIF4G to bind eIF4E (Altmann et al 1997;Ptushkina et al 1998;Cosentino et al 2000).…”

“…The 4E-BPs regulate a variety of cellular and developmental processes in higher eukaryotes (Kong and Lasko 2012). Yeast has two characterized 4E-BPs that contain the consensus eIF4E-binding motif, Caf20 (also called p20) and Eap1, which are 18 and 70 kDa, respectively (Altmann et al 1997;Cosentino et al 2000). Caf20 and Eap1 share no sequence similarity outside the eIF4E-binding motif, mutation of which abrogates eIF4E interactions (Altmann et al 1997;Cosentino et al 2000;Ibrahimo et al 2006).…”

The target of rapamycin (TOR) proteins

“…The mechanism for this translational repression is not understood, but could be due, at least in some strains, to the degradation of the initiation factor eIF4G (51,52). A putative regulator of yeast eIF4E function, termed Eap1p (eIF4E-associated protein 1), may also be involved in this process, as disruption of the EAP1 gene results in partial rapamycin resistance (53). The G 1 arrest in response to Tor inactivation was suggested to be due to the inhibition of translation of an mRNA coding for a cyclin involved in G 1 to S progression, CLN3, because the cell cycle block can be overcome by forced expression of CLN3 (54)(55)(56).…”