Poly(A)-binding proteins regulate both mRNA deadenylation and decapping inyeast cytoplasmic extracts

The pathway of mRNA degradation has been extensively studied in the yeast, Saccharomyces, cerevisiae, and it is now clear that many mRNAs decay by a d eadenylation-dependent mechanism. Although several of the factors required for mRNA decay have been identified, the regulation and: precise roles of m any of the proteins involved remains unclear. We have developed an in vitro system that recapitulates both the deadenylation and the decapping steps o f mRNA decay. Furthermore, both deadenylation and decapping are inhibited b y poly(A) binding proteins in our assay. Our system has allowed us to separ ate the decay process from translation and we have shown that the poly(A) t ail is capable of inhibiting decapping in an elF4E-independent manner. Our in vitro system should prove invaluable in dissecting the mechanisms of mRN A turnover.