Nuclear receptors for steroids, thyroid hormones and retinoic acids are ligand-dependent transcription factors that activate transcription through specific DNA binding sites in their target genes. Several related transcriptional coactivators and corepressors have been described that work in concert with the steroid receptor family to either induce or repress transcription from hormone-responsive elements. This family includes GRIP1 (for GR interacting protein 1, also designated NCoA-2 or Tif2); SRC-1 (for steroid receptor coactivator-1, also designated NCoA-1); RAC3 (also designated AIB1, for amplified in breast cancer, or ACTR), which displays elevated expression in estrogen receptor positive ovarian and breast cancers; and p/CIP (for p300/CBP/Co-Integrator Protein), which is required for the transcriptional activation of p300/CBP-dependent transcription factors. The nuclear receptor coactivator 1 (NCOA1) is a transcriptional coregulatory protein that contains several nuclear receptor interacting domains and an intrinsic histone acetyltransferase activity. NCOA1 is recruited to DNA promotion sites by ligand-activated nuclear receptors. NCOA1, in turn, acylates histones, which makes downstream DNA more accessible to transcription. Hence, NCOA1 assists nuclear receptors in the upregulation of DNA expression. NCOA1 is also frequently called steroid receptor coactivator-1 (SRC-1).