TRANSLATION INITIATION-FACTOR EIF4G MEDIATES IN-VITRO POLY(A) TAIL-DEPENDENT TRANSLATION

The yeast translation factor eIF4G associates with both the cap-bindin g protein eIF4E and the poly(A)-binding protein Pab1p. Here we report that the two yeast eIF4G homologs, Tif4631p and Tif4632p, share a cons erved Pab1p-binding site. This site is required for Pab1p and poly(A) tails to stimulate the in vitro translation of uncapped polyadenylylat ed mRNA, and the region encompassing it is required for the cap and th e poly(A) tail to synergistically stimulate translation, This region o n Tif4631p becomes essential for cell growth when the eIF4E binding si te on Tif4631p is mutated. Pab1p mutations also show synthetic lethal interactions with eIF4E mutations, These data suggest that eIF4G media tes poly(A) tail stimulated translation in vitro, and that Pab1p and t he domain encompassing the Pab1p-binding site an eIF4G can compensate for partial loss of eIF4E function in vivo.