Decapping scavenger enzyme that catalyzes the cleavage of a residual cap structure following the degradation of mRNAs by the 3'->5' exosome-mediated mRNA decay pathway. Hydrolyzes cap analog structures like 7-methylguanosine nucleoside triphosphate (m7GpppG) with up to 10 nucleotide substrates (small capped oligoribonucleotides) and specifically releases 5'-phosphorylated RNA fragments and 7-methylguanosine monophosphate (m7GMP). Cleaves cap analog structures like tri-methyl guanosine nucleoside triphosphate (m3(2,2,7)GpppG) with very poor efficiency. Does not hydrolyze unmethylated cap analog (GpppG) and shows no decapping activity on intact m7GpppG-capped mRNA molecules longer than 25 nucleotides. Does not hydrolyze 7-methylguanosine diphosphate (m7GDP) to m7GMP. May also play a role in the 5'->3 mRNA decay pathway; m7GDP, the downstream product released by the 5'->3' mRNA mediated decapping activity, may be also converted by DCPS to m7GMP. Binds to m7GpppG and strongly to m7GDP. Plays a role in first intron splicing of pre-mRNAs. Inhibits activation-induced cell death. a 5'-end (N(7)-methyl 5'-triphosphoguanosine)-ribonucleoside in mRNA + H2O = a 5'-end diphospho-ribonucleoside in mRNA + 2 H(+) + N(7)-methyl-GMP The hydrolytic product 7-methylguanosine diphosphate (m7GDP) efficiently inhibits the decapping scavenger activity and acts as a competitive inhibitor in vitro. Inhibited by 2,4-diaminoquinazoline. Homodimer. Associates with components of the exosome multienzyme ribonuclease complex, such as EXOSC3 and EXOSC4. Interacts with NDOR1. Predominantly localized in the nucleus. Nucleocytoplasmic shuttling protein that can transiently enter the cytoplasm in mammalian cells in a XPO1/CRM1-dependent manner. The C-terminal histidine triad (HIT) motif and the N-terminal domain are required for the decapping activity. The N-terminus is necessary but not sufficient for binding cap structures. Belongs to the HIT family.