| BRCA1 regulates transcription, and this function may be at the root of its diverse cellular activities and tissue-specific tumor suppression. A number of gene targets of BRCA1 have been identified, but little is understood about the mechanisms by which BRCA1 activates and represses transcription. The work in this dissertation describes distinct biochemical mechanisms for transcriptional activation and repression by BRCA1. BRCA1/BARD1 ubiquitinate the large subunit of RNA Polymerase II (Rpb1), and we developed a fully-purified transcription/ubiquitination assay to ask whether the enzymatic activity of RNA Polymerase II was regulated by this modification. This assay demonstrates that ubiquitination of the pre-initiation-complex (PIC) by BRCA1/BARD1 induces dissociation of TFIIE, leading to a failure of initiation. BRCA1 also can stimulate transcription, independent of its E3 ubiquitin ligase activity. By stabilizing properly initiated PICs, BRCA1 promotes productive transcriptional initiation. In the cell, these opposing activities are likely regulated by interacting transcription factors that participate in combinatorial regulation of specific gene targets with BRCA1. |
