Translation initiation factor eIF4G mediates in vitro poly(A) tail-dependent translation

Abstract

The yeast translation factor eIF4G associates with both the cap-binding protein eIF4E and the poly(A)-binding protein Pab1p. Here we report that the two yeast eIF4G homologs, Tif4631p and Tif4632p, share a conserved Pab1p-binding site. This site is required for Pab1p and poly(A) tails to stimulate the in vitro translation of uncapped polyadenylylated mRNA, and the region encompassing it is required for the cap and the poly(A) tail to synergistically stimulate translation. This region on Tif4631p becomes essential for cell growth when the eIF4E binding site on Tif4631p is mutated. Pab1p mutations also show synthetic lethal interactions with eIF4E mutations. These data suggest that eIF4G mediates poly(A) tail stimulated translation in vitro, and that Pab1p and the domain encompassing the Pab1p-binding site on eIF4G can compensate for partial loss of eIF4E function in vivo.

Conducting the initiation of protein synthesis: the role of eIF4G

“…This suggests that interaction of eIF4G to the 5' end of the mRNA can be promoted by either eIF4E or PABP. Consistent with this hypothesis, the poly(A) tail alone can deliver 40 S ribosomal subunits on an mRNA devoid of a cap structure in a yeast cell-free translation system Tarun et al, 1997).…”

“…The main interaction site in mammals is located within the extended N-terminal sequence of eIF4GI (see Fig. 2) and is conserved in eIF4GII, but does not exhibit any sequence homology with the yeast PABP interacting domain except for a rich content of basic amino acids (Imataka et al, 1998;Tarun et al, 1997).…”

Starting the protein synthesis machine: eukaryotic translation initiation

“…(69)(70)(71)(72) In a yeast cell-free system, the poly(A) tail, like the cap structure, was able to support the recruitment of the 40S ribosomal subunit by itself to an uncapped mRNA. (73) This function of the poly(A) tail as well as the functional synergy with the cap structure requires the poly(A)-binding protein (PABP) (73) and its interaction with the N-terminal part of eIF4G (74,75) (Fig. 3).…”

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

“…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).…”