Compositions of matter consisting of a family of related nucleotide sequences that encode proteins, termed BRCA1 Modulator Proteins, that bind to the tumor suppressor gene product BRCA1, and methods of using the nucleotide sequences and the proteins encoded thereby, to diagnose and/or treat disease where the BRCA1 Modulator Proteins have an apparent molecular weight of 45-97 kdaltons and are characterized by having at least one leucine zipper domain, and optionally a zinc finger domain.