Nuclear receptor coactivator 1, also named SRC-1, directly binds nuclear receptors and stimulates transcriptional activities in a hormone-dependent fashion. Involved in the coactivation of different nuclear receptors, such as for steroids (PGR, GR, and ER), retinoids (RXRs), thyroid hormone (TRs), and prostanoids (PPARs). Also involved in coactivation mediated by STAT3, STAT5A, STAT5B, and STAT6 transcription factors. Displays histone acetyltransferase activity toward H3 and H4; the relevance of such activity remains however unclear. Plays a central role in creating multisubunit coactivator complexes that act via the remodeling of chromatin, and possibly act by participating in both chromatin remodeling and recruitment of general transcription factors. Required with NCOA2 to control energy balance between white and brown adipose tissues. Required for mediating steroid hormone response. Isoform 2 has a higher thyroid hormone-dependent transactivation activity than isoform 1 and isoform 3.