Necessary for the degradation of mRNAs, both in normal mRNA turnover and in nonsense-mediated mRNA decay (PubMed:12417715). Removes the 7-methyl guanine cap structure from mRNA molecules, yielding a 5'-phosphorylated mRNA fragment and 7m-GDP (PubMed:12417715). Contributes to the transactivation of target genes after stimulation by TGFB1 (PubMed:11836524). Essential for embryonic development (PubMed:33813271). 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 Forms a complex with EDC3, DCP2, DDX6 and EDC4/HEDLS, within this complex directly interacts with EDC3 (PubMed:16364915). Part of a cytoplasmic complex containing proteins involved in mRNA decay, including XRN1 and LSM1 (PubMed:12515382). Interacts with DCP1B (PubMed:12417715). Interacts with DCP2 (PubMed:12417715). Interacts with DDX17 in an RNA-independent manner (PubMed:21876179). Interacts with PNRC2 (PubMed:19150429). Interacts with SMAD4 (PubMed:11836524). Interacts with UPF1 (PubMed:12417715). Interacts with ZC3HAV1 (PubMed:21876179). Interacts with ZFP36L1 (PubMed:15687258). Interacts with NBDY (PubMed:27918561). Interacts with DHX34; the interaction is RNA-independent (PubMed:25220460). Co-localizes with NANOS3 in the processing bodies (By similarity). Predominantly cytoplasmic, in processing bodies (PB) (PubMed:16364915). Nuclear, after TGFB1 treatment. Translocation to the nucleus depends on interaction with SMAD4 (PubMed:11836524). Detected in heart, brain, placenta, lung, skeletal muscle, liver, kidney and pancreas. Belongs to the DCP1 family.