Nuclear receptor coactivator that directly binds nuclear receptors and stimulates the transcriptional activities in a hormone-dependent fashion. Plays a central role in creating a multisubunit coactivator complex; which probably acts via remodeling of chromatin. Involved in the coactivation of different nuclear receptors; such as for steroids (GR and ER); retinoids (RARs and RXRs); thyroid hormone (TRs); vitamin D3 (VDR) and prostanoids (PPARs). Displays histone acetyltransferase activity. Also involved in the coactivation of the NF-kappa-B pathway via its interaction with the NFKB1 subunit.