ASSOCIATION OF THE YEAST POLY(A) TAIL BINDING-PROTEIN WITH TRANSLATION INITIATION-FACTOR EIF-4G

Although the cap structure and the poly(A) tail are on opposite ends o f the mRNA molecule, previous work has suggested that they interact to enhance translation and inhibit mRNA degradation. Here we present bio chemical data that show that the proteins bound to the mRNA cap (eIF-4 F) and poly(A) tail (Pab1p) are physically associated in extracts from the yeast Saccharomyces cerevisiae. Specifically, we find that Pab1p co-purifies and to-immunoprecipitates with the eIF-4G subunit of eIF-4 F. The Pab1p binding site on the recombinant yeast eIF-4G protein Tif4 632p was mapped to a 114-amino-acid region just proximal to its eIF-4E binding site. Pab1p only bound to this region when complexed to poly( A). These data support the model that the Pab1p-poly(A) tail complex o n mRNA can interact with the cap structure via eIF-4G.