A split active site couples cap recognition by Dcp2 to activation

Decapping by Dcp2 is an essential step in 5′-3 ′ mRNA decay. In yeast, decapping requires an open-to-closed transition in Dcp2, though the link between closure and catalysis remains elusive. Here we show using NMR that cap binds conserved residues on both the catalytic and regulatory domains of Dcp2. Lesions in the cap-binding site on the regulatory domain reduce the catalytic step two orders of magnitude and block formation of the closed state whereas Dcp1 enhances the catalytic step by a factor of ten and promotes closure. We conclude that closure occurs during the rate-limiting catalytic step of decapping, juxtaposing the cap-binding region of each domain to form a composite active site. This work suggests a model for regulation of decapping, where coactivators trigger decapping by stabilizing a labile composite active site. Degradation of messenger RNA plays a crucial role in animal development1, cell proliferation2,3, differentiation4, stress responses5, the adaptive immune system6, and transcript quality control7. Removal of the 5′-terminal cap structure by the mRNA decapping enzyme Dcp2 is a critical step in numerous 5′–3 ′ decay pathways including bulk 5′–3 ′ decay8,9, AU-rich element mediated decay10,11, nonsense-mediated deca