Decapping enzyme for NAD-capped RNAs: specifically hydrolyzes the nicotinamide adenine dinucleotide (NAD) cap from a subset of RNAs by removing the entire NAD moiety from the 5′-end of an NAD-capped RNA (PubMed:28283058). The NAD-cap is present at the 5′-end of some RNAs and snoRNAs (PubMed:28283058). In contrast to the canonical 5′-end N7 methylguanosine (m7G) cap, the NAD cap promotes mRNA decay (PubMed:28283058). Preferentially acts on NAD-capped transcripts in response to environmental stress (PubMed:31101919). Also acts as a non-canonical decapping enzyme that removes the entire cap structure of m7G capped or incompletely capped RNAs and mediates their subsequent degradation (By similarity). Specifically degrades pre-mRNAs with a defective 5′-end m7G cap and is part of a pre-mRNA capping quality control (By similarity). Has decapping activity toward incomplete 5′-end m7G cap mRNAs such as unmethylated 5′-end-capped RNA (cap0), while it has no activity toward 2′-O-ribose methylated m7G cap (cap1) (PubMed:29601584). In contrast to canonical decapping enzymes DCP2 and NUDT16, which cleave the cap within the triphosphate linkage, the decapping activity releases the entire cap structure GpppN and a 5′-end monophosphate RNA (By similarity). Also has 5′-3′ exoribonuclease activities: The 5′-end monophosphate RNA is then degraded by the 5′-3′ exoribonuclease activity, enabling this enzyme to decap and degrade incompletely capped mRNAs (PubMed:29601584). Also possesses RNA 5′-pyrophosphohydrolase activity by hydrolyzing the 5′-end triphosphate to release pyrophosphates (By similarity). Exhibits decapping activity towards FAD-capped RNAs (PubMed:32374864). Exhibits decapping activity towards dpCoA-capped RNAs in vitro (By similarity).
