BRCA1 Associated RING Domain gene 1 (BARD1) interacts with the N terminal region of BRCA1. In addition to its ability to bind BRCA1 in vivo and in vitro, BARD1 shares homology with the 2 most conserved regions of BRCA1: the N terminal RING motif and the C terminal BRCT domain. The RING motif is a cysteine rich sequence found in a variety of proteins that regulate cell growth, including the products of tumor suppressor genes and dominant protooncogenes. The BARD1 protein also contains 3 tande