Structures of ring domains in the RBR segments. The structure graphics were generated with the program VMD . The backbone trace and the secondary structure are shown as ribbons and the zinc ions as red spheres. (a) Carboxy-terminal part of the RBR region (C-RING) in the human Ariadne-1 homolog protein HHARI (PDB accession number 1WD2; residues 326-395 of UNIPROT accession number Q9Y4X5; subfamily A1/Ari1). (b) The N-RING of the RBR segment of the human UbcM4-interacting protein 4 (PDB accession number 1WIM; residues 20-100 of UNIPROT accession number P50876; subfamily C/RNF144).