Catalytic component of the decapping complex necessary for the degradation of mRNAs, both in normal mRNA turnover and in nonsense-mediated mRNA decay. Removes the 7-methyl guanine cap structure from mRNA molecules, yielding a 5'-phosphorylated mRNA fragment and 7m-GDP. Decapping is the major pathway of mRNA degradation in yeast. It occurs through deadenylation, decapping and subsequent 5' to 3' exonucleolytic decay of the transcript body (By similarity). Component of the decapping complex. Is concentrated in several cytoplasmic foci called P bodies (or cytoplasmic processing bodies) which represent sites of mRNA decapping and 5' to 3' exonucleotidic decay. Belongs to the Nudix hydrolase family. DCP2 subfamily.