Conservation of the IBR domain. (a) Structures of IBR domains solved to date from RNF31 (left) (PDB ID 2CT7) and Parkin (right) (PDB ID 2JMO). (b) Multiple sequence alignment of the IBR domain from human RBR ligases. Residue numbers are shown at the beginning of the alignment. Sequences were aligned using CLUSTALW . Swiss-Prot numbers for sequences used in multiple sequence alignments are as follows: Cullin-9: Q81WT3, Parkin: O60260, ANKIB1: Q9P2G1, ARIH1: Q9Y4X5, ARIH2: O95376, RBCK1: Q9BYM8, RNF144A: P50876, RNF144B:Q7Z419, RNF19A:Q9NV58, RNF19B: Q6ZMZ0, RNF216: Q9NWF9, RNF14: Q9UBS8, and RNF31: Q96EP0.