Interaction between a poly(A)-specific ribonuclease and the 5 ' cap influences mRNA deadenylation rates in vitro

We have used an in vitro system that reproduces in vivo aspects of mRNA tur nover to elucidate mechanisms of deadenylation. DAN, the major enzyme respo nsible for poly(A) tail shortening in vitro, specifically interacts with th e 5' cap structure of RNA substrates, and this interaction is greatly stimu lated by a poly(A) tail. Several observations suggest that cap-DAN interact ions are functionally important for the networking between regulated mRNA s tability and translation. First, uncapped RNA substrates are inefficiently deadenylated. Second, a stem-loop structure in the 5' UTR dramatically redu ces deadenylation by interfering with cap-DAN interactions. Third, the addi tion of cap binding protein eIF4E inhibits deadenylation in vitro. These da ta provide insights into the early steps of substrate recognition that targ et an mRNA for degradation.