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). Has a role in primitive myelopoiesis in the differentiation of granulocytes and macrophages. May play a role in the positive regulation of the circadian clock (By similarity). Interacts with the thyroid hormone receptors thraa and thrb (via the ligand-binding domain). Expressed ubiquitously in the embryo and in many adult tissues including the brain, gills, liver, swim bladder and skin. Shows highest expression in the ovary and testis, and lower expression in the intestine, eye and skin. Only isoform E20b is expressed in the muscle and heart. Contains 3 Leu-Xaa-Xaa-Leu-Leu (LXXLL) motifs. The LXXLL motifs are essential for the association with nuclear receptors and are, 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.