These domains are found in the eukaryotic proteins typified by the Nedd4-binding protein 1 and the bacterial YacP-like proteins (Nedd4-BP1, YacP nucleases; NYN domains). The NYN domain shares a common protein fold with two other previously characterized groups of nucleases, namely the PIN (PilT N-terminal) and FLAP/5' --> 3' exonuclease superfamilies. These proteins share a common set of 4 acidic conserved residues that are predicted to constitute their active site. Based on the conservation of the acidic residues and structural elements Aravind and colleagues suggest that PIN and NYN domains are likely to bind only a single metal ion, unlike the FLAP/5' --> 3' exonuclease superfamily, which binds two metal ions. Based on conserved gene neighborhoods Aravind and colleagues infer that the bacterial members are likely to be components of the processome/degradsome that process tRNAs or ribosomal RNAs.

1: The NYN Domains: Novel Predicted RNAses with a PIN Domain-Like Fold. Anantharaman V, Aravind L; RNA Biol. 2006; [Epub ahead of print] PMID:17114934