Cap-dependent deadenylation of mRNA

Poly(A) tail removal is often the initial and rate-limiting step in mRNA de cay and is also responsible for translational silencing of maternal mRNAs d uring oocyte maturation and early development, Here we report that deadenyl ation in HeLa cell extracts and by a purified mammalian poly(A)-specific ex oribonuclease, PARN (previously designated deadenylating nuclease, DAN), is stimulated by the presence of an m(7)-guanosine cap on substrate RNAs, Kno wn cap-binding proteins, such as eIF4E and the nuclear cap-binding complex, are not detectable in the enzyme preparation, and PARN itself binds to m(7 )GTP-Sepharose and is eluted specifically with the cap analog m(7)GTP. Xeno pus PARN is known to catalyze mRNA deadenylation during oocyte maturation, The enzyme is depleted from oocyte extract with m7GTP-Sepharose, can be pho tocrosslinked to the m(7)GpppG cap and deadenylates m(7)GpppG-capped RNAs m ore efficiently than ApppG-capped RNAs both in vitro and in vivo. These dat a provide additional evidence that PARN is responsible for deadenylation du ring oocyte maturation and suggest that interactions between 5' cap and 3' poly(A) tail may integrate translational efficiency with mRNA stability.