A common function for mRNA 5' and 3' ends in translation initiation in yeast.

The mRNA poly(A) tail and its associated poly(A) binding protein (Pab1p) are ubiquitous in eukaryotes. The function of the poly(A) tail is to stabilize mRNA and to stimulate its translation. The development of a poly(A)- and cap-dependent yeast in vitro translation system has allowed us to understand how poly(A) stimulates translation. We find that Pab1p but not the cap binding protein eIF-4E is required for poly(A) tail-dependent translation, and that the Pab1p-poly(A) tail complex functions to recruit the 40S ribosomal subunit to the mRNA. These data introduce a new step into the pathway of translation initiation and merge the translational functions of the two ends of mRNA.