Isolation and characterization of Dcp1p, the yeast mRNA decapping enzyme.

A major mechanism of mRNA decay occurs by the process of deadenylation, decapping and 5' --> 3' exonucleolytic degradation. Recently, the product of the DCP1 gene has been shown to be required for decapping mRNAs in vivo and co-purifies with decapping activity in vitro. We have purified Dcp1p to homogeneity and shown that it is sufficient for decapping, thereby indicating that Dcp1p is the decapping enzyme. Characterization of Dcp1p activity in vitro indicated that the 7-methyl group of the cap structure contributes to the enzyme's substrate specificity. In addition, Dcp1p was effectively inhibited by uncapped mRNAs, and the enzyme efficiently cleaved substrates that were >/=25 nucleotides in length, with a preference for longer mRNA substrates. These properties suggest that Dcp1p recognizes the mRNA substrate by interactions with both the cap and the RNA moiety. The Dcp1p is also a phosphoprotein, suggesting its activity may be regulated by post-transcriptional modification