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:30949699). The NAD-cap is present at the 5'-end of some RNAs and promotes mRNA decay (By similarity). Its precise role is unclear: may be involved in the connection between RNA turnover and retrograde chloroplast-to-nucleus signaling independently of its deNADding activity (PubMed:30949699). a 5'-end NAD(+)-phospho-ribonucleoside in mRNA + H2O = a 5'-end phospho-ribonucleoside in mRNA + H(+) + NAD(+) Binds 2 magnesium ions. A number of isoforms are produced. According to EST sequences. Growth and pigmentation defects associated with global transcriptomic changes and accumulation of RNA quality control siRNAs. Belongs to the DXO/Dom3Z family. In contrast to other members of the family, shows reduced activity toward of m7G capped or incompletely capped RNAs, probably caused by the presence of an Asn residue in position 298 instead of a Gly (PubMed:30949699). The presence of an Asn-298 does not affect the decapping activity on NAD-cap RNAs (PubMed:30949699). The predicted gene At4g17620 has been split into 3 genes: At4g17615, At4g17616 and At4g17620. The predicted gene At4g17620 has been split into 3 genes: At4g17615, At4g17616 and At4g17620.