BRCA1 (breast and ovarian cancer susceptibility protein 1) is a nuclear phosphoprotein that plays a role in maintaining genomic stability and acts as a tumor suppressor. It combines with other tumor suppressors, DNA damage sensors, and signal transducers to form a large multi-subunit protein complex known as BASC (for BRCA1 associated genome surveillance complex). BRCA1 associates with RNA polymerase II, and through the C terminal domain, also interacts with histone deacetylase complex. This protein thus plays a role in transcription, DNA repair of double-stranded breaks, and recombination. Mutations in the BRCA1 gene are responsible for approximately 40% of inherited breast cancers and more than 80% of inherited breast and ovarian cancers. Alternative splicing plays a role in modulating the subcellular localization and physiological function of this gene. Many alternatively spliced transcript variants have been described for this gene but only some have had their full length natures identified.