The IBR (In Between Ring fingers) domain is often found to occur between pairs of ring fingers (Pfam:PF00097). This domain has also been called the C6HC domain and DRIL (for double RING finger linked) domain [2]. Proteins that contain two Ring fingers and an IBR domain (these proteins are also termed RBR family proteins) are thought to exist in all eukaryotic organisms. RBR family members play roles in protein quality control and can indirectly regulate transcription [3]. Evidence suggests that RBR proteins are often parts of cullin-containing ubiquitin ligase complexes. The ubiquitin ligase Parkin is an RBR family protein whose mutations are involved in forms of familial Parkinson's disease [3][4].

1: A novel transactivation domain in parkin. Morett E, Bork P; Trends Biochem Sci 1999;24:229-231. PMID:10366851

2: TRIADs: a new class of proteins with a novel cysteine-rich signature. van der Reijden BA, Erpelinck-Verschueren CA, Lowenberg B, Jansen JH; Protein Sci 1999;8:1557-1561. PMID:10422847

3: Parkin and relatives: the RBR family of ubiquitin ligases. Marin I, Lucas JI, Gradilla AC, Ferrus A; Physiol Genomics 2004;17:253-263. PMID:15152079

4: Comparative genomics of the RBR family, including the Parkinson's disease-related gene parkin and the genes of the ariadne subfamily. Marin I, Ferrus A; Mol Biol Evol 2002;19:2039-2050. PMID:12446796

5: Structure of the C-terminal RING finger from a RING-IBR-RING/TRIAD motif reveals a novel zinc-binding domain distinct from a RING. Capili AD, Edghill EL, Wu K, Borden KL; J Mol Biol. 2004;340:1117-1129. PMID:15236971