The protein BARD1 and BRCA1 form a heterodimer via their N-terminal RING finger domains that could be observed in vivo and in vitro.
The human BARD1 protein is 777 amino acids long and contains a RING finger domain (residues 46-90), four ankyrin repeats (residues 420-555), and two tandem BRCT domains (residues 568-777). BARD1 and BRCA1 form a heterodimer via their N-terminal RING finger domains. The BARD1-BRCA1 interaction is observed in vivo and in vitro and is essential for BRCA1 stability. 
