The RING domain of the breast and ovarian cancer tumour-suppressor BRCA1 interacts with multiple cognate proteins, including the RING protein BARD1. Proper function of the BRCA1 RING domain is critical, as evidenced by the many cancer-predisposing mutations found within this domain. A dimer is formed between the RING domains of BRCA1 and BARD1. The BRCA1-BARD1 structure provides a model for its ubiquitin ligase activity, illustrates how the BRCA1 RING domain can be involved in associations with multiple protein partners and provides a framework for understanding cancer-causing mutations at the molecular level [1]. The corresponding BRCA1-RING domain is on family zf-C3HC4_2, Pfam:PF13923.

1: Structure of a BRCA1-BARD1 heterodimeric RING-RING complex. Brzovic PS, Rajagopal P, Hoyt DW, King MC, Klevit RE; Nat Struct Biol. 2001;8:833-837. PMID:11573085