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). {ECO:0000269|PubMed:11836524, ECO:0000269|PubMed:12417715, ECO:0000269|PubMed:33813271}. This is the function of Ensembl gene identifier ENSG00000272886 (DCP1A, decapping mRNA 1A).