Transcriptional coactivator for steroid receptors and nuclear receptors. Coactivator of the steroid binding domain (AF-2) but not of the modulating N-terminal domain (AF-1) (By similarity). Required in a nuclear receptor pathway to suppress expression of dorsal mesoderm genes. May play a role in the positive regulation of the circadian clock (By similarity). Expressed homogeneously during late blastula-early gastrula stages, becoming highly expressed in the notochord in the late gastrula and neurula stages. At hatching, restricted to a few areas including the blood precursor region, prospective pronephros and retina. Contains three Leu-Xaa-Xaa-Leu-Leu (LXXLL) motifs. The LXXLL motifs are essential for the association with nuclear receptors and, at least in part, functionally redundant (By similarity). The LLXXLXXXL motif is involved in transcriptional coactivation and CREBBP/CBP binding. Contains 2 C-terminal transcription activation domains (AD1 and AD2) that can function independently. Belongs to the SRC/p160 nuclear receptor coactivator family.