Abstract: The RING finger is a zinc-binding domain that is found in proteins from plants to humans, but whose function remains largely enigmatic. The domain itself is distinct from other zinc-finger motifs in terms of sequence homology, zinc-ligation scheme and three-dimensional structure. It appears that the RING is involved in mediating protein-protein interactions and in some cases multi-protein complexes, which might depend on the presence of other proteins and/or domains.