Catalytic component of the decapping complex necessary for the degradation of mRNAs, both in normal mRNA turnover and in nonsense-mediated mRNA decay (PubMed:10508173, PubMed:11139489, PubMed:11741542). Removes the 7-methyl guanine cap structure from mRNA molecules, yielding a 5'-phosphorylated mRNA fragment and 7m-GDP (PubMed:12554866). Decapping is the major pathway of mRNA degradation in yeast and occurs through deadenylation, decapping and subsequent 5' to 3' exonucleolytic decay of the transcript body (PubMed:10508173, PubMed:11139489, PubMed:11741542). Blocks autophagy in nutrient-rich conditions by repressing the expression of ATG-related genes through degradation of their transcripts (PubMed:19779198). a 5'-end (N(7)-methyl 5'-triphosphoguanosine)-ribonucleoside in mRNA + H2O = a 5'-end phospho-ribonucleoside in mRNA + 2 H(+) + N(7)-methyl-GDP Component of the decapping complex composed of DCP1 and DCP2 (PubMed:10508173, PubMed:11741542, PubMed:14758354). Interacts with mRNA, LSM2, LSM4 and LSM8 (PubMed:10900456). Interacts with EDC3 (PubMed:18678652). Increases autophagy activity through accumulation of autophagy-related proteins in nutrient-replete conditions (PubMed:19779198). Present with 8530 molecules/cell in log phase SD medium. Belongs to the Nudix hydrolase family. DCP2 subfamily.