The breast cancer and ovarian cancer susceptibility gene BRCA1 encodes a nucleoprotein whose mutations or aberrant expression is associated with both inherited and sporadic cancers. Studies over the last 6 years have suggested that BRCA1 may function as a scaffold in the assembly of a multi-protein complex, which plays a role in gene transcription, DNA damage repair, and transcription-coupled DNA damage repair. In this review, we discuss the implications drawn from the studies of BRCA1-interacting proteins and the cellular signaling pathways that may be involved in controlling the functions of BRCA1.