A COMMON FUNCTION FOR MESSENGER-RNA-5' AND MESSENGER-RNA-3' ENDS IN TRANSLATION INITIATION IN YEAST

The mRNA poly(A) tail and its associated poly(A) binding protein (Pab1 p) are ubiquitous in eukaryotes. The function of the poly(A) tail is t o stabilize mRNA and to stimulate its translation The development of a poly(A)- and cap-dependent yeast in vitro translation system has allo wed 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) t ail dependent translation, and that the Pab1p-poly(A) tail complex fun ctions to recruit the 40S ribosomal subunit to the mRNA. These data in troduce a new step into the pathway of translation initiation and merg e the translational functions of the two ends of mRNA.