Translation Initiation Factors eIF-iso4G and eIF-4B Interact with the Poly(A)-binding Protein and Increase Its RNA Binding Activity

Abstract

The 5-cap and the poly(A) tail act synergistically to increase the translational efficiency of eukaryotic mRNAs, which suggests that these two mRNA elements communicate during translation. We report here that the cap-associated eukaryotic initiation factors (eIFs), i.e. the two isoforms of the cap-binding complex (eIF-4F and eIF-iso4F) and eIF-4B, bind to the poly(A)-binding protein (PABP) both in the presence and absence of poly(A) RNA. The interactions between PABP and eIF-4F, eIF-iso4F, and eIF-4B were measured in the absence of poly(A) RNA using far Western analysis and confirmed by direct fluorescence titration studies. The functional consequence of the interaction between these initiation factors and PABP was examined using RNA binding assays and RNA mobility shift analysis. eIF-4F, eIF-iso4F, and eIF-4B promoted PABP activity through a shift in its equilibrium affinity for poly(A). eIF-iso4G, the large subunit of eIF-iso4F, was the subunit responsible for the interaction between eIF-iso4F and PABP and was the subunit that promoted PABP RNA binding activity. Truncation analysis of eIF-iso4G indicated that a domain close to its N-terminal end appeared to be involved in binding PABP. These results suggest that the interaction between PABP and eIF-4B and eIF-iso4G may be involved in mediating the functional co-dependence observed between the cap and the poly(A) tail during translation.Most eukaryotic mRNAs contain a cap (m 7

Degradation of eukaryotic polypeptide chain initiation factor (eIF) 4G in response to induction of apoptosis in human lymphoma cell lines

“…We did, however, observe a complete loss of the PABP that co-puri®ed with eIF4E after antiFas treatment (Figure 9c; compare lanes 5 and 6). The latter result may indicate that PABP associates with eIF4G in mammalian eIF4F complexes, as is the case in yeast (Tarun and Sachs, 1996;Le et al, 1997), or that interaction of PABP with the eIF4G homologue PAIP (Craig et al, 1998) is also altered in cells undergoing apoptosis. The e ects of anti-Fas treatment on eIF4G and the co-puri®cation of PABP with eIF4E were blocked by Z-VAD.FMK (Figure 9c, lanes 2 vs 3 and lanes 6 vs 7), under conditions where this agent prevented the apoptotic response as measured by PARP cleavage (Figure 9a) or the appearance of cells with less than the G1 content of DNA (Figure 9b).…”

“…The stability of eIF4G may be determined not only by the signalling pathways by which cells respond to stresses but also by the other proteins with which the factor associates. Binding sites for eIF4E, eIF4A, eIF3 and PABP have been characterized on eIF4G from various eukaryotic sources (Tarun and Sachs, 1996;Morley et al, 1997;Le et al, 1997;. The in¯uence of these proteins on eIF4G stability in vivo remains unknown.…”

“…Recently a second form of human eIF4G has also been described (Gradi et al, 1998). eIF4G possesses domains for the binding of eIF4E and eIF3 in the N-terminal and central parts of its sequence respectively, and it also has binding sites for eIF4A (Lamphear et al, 1995; and, at least in yeast, for the poly(A) binding protein (PABP) (Tarun and Sachs, 1996;Le et al, 1997;Tarun et al, 1997). Interaction of PABP with eIF4G or with the recently discovered eIF4G homologue PAIP (Craig et al, 1998) may allow functional association of the 3' end of an mRNA with the 5' end, thus e ectively causing`circularization' of the mRNA during protein synthesis (Tarun et al, 1997).…”

Starting the protein synthesis machine: eukaryotic translation initiation

“…Adding eIF4E, eIF4G, PABP, and a capped and polyadenylated mRNA together in vitro resulted in the formation of pseudocircular complexes. (81) PABP and eIF4G also interact in plant (82) and mammalian cells. (83,84) Interestingly, there is no apparent sequence homology between the PABP-binding regions of yeast and mammalian eIF4G, despite the evolutionary conservation of the eIF4G-PABP interaction.…”

A GG Nucleotide Sequence of the 3′ Untranslated Region of Amyloid Precursor Protein mRNA Plays a Key Role in the Regulation of Translation and the Binding of Proteins

“…This complex is supposed to promote the initiation of translation of capped mRNA by promoting the recruitment of the 40S ribosomal subunit (40). In addition, the PABP was also demonstrated to interact with eukaryotic initiation factors (11,17). The interaction of PABP with different components of the preinitiation complex of translation might explain why a sequence located downstream of a coding region is able to control translation.…”