Catalyzes the asymmetric hydrolysis of diadenosine 5',5'''- P1,P4-tetraphosphate (Ap4A) to yield AMP and ATP (By similarity). Exhibits decapping activity towards FAD-capped RNAs and dpCoA-capped RNAs in vitro (By similarity). {ECO:0000250|UniProtKB:P50584, ECO:0000250|UniProtKB:P56380}. This is the function of NUDT2 (nudix hydrolase 2, ENSG00000164978).