Co-factor of BRCA1, also known as COBRA1, was first identified as a protein that binds to the tumour suppressor protein encoded by the breast cancer susceptibility gene BRCA1 (1). It was subsequently found to be identical to subunit B of the Negative Elongation Factor (NELF) complex (2). NELF is composed of four subunits (A, B, C or D, and E) and plays a pivotal role in the transcriptional pausing of RNA polymerase II.
