Transcriptional coactivator for creb1 which activates transcription through both consensus and variant cAMP response element (CRE) sites. Acts as a coactivator, in the SIK/TORC signaling pathway, being active when dephosphorylated and acts independently of creb1 'Ser-119' phosphorylation. Enhances the interaction of creb1 with taf4. Regulates the expression of specific CREB-activated genes such as the steroidogenic gene, StAR. Potent coactivator of ppargc1a and inducer of mitochondrial biogenesis in muscle cells (By similarity). Binding, as a tetramer, through its N-terminal region, with the bZIP domain of creb1 enhances recruitment of taf4 to the promoter. 'Arg-300' in the bZIP domain of creb1 is essential for this interaction (By similarity). Appears to be mainly nuclear. Belongs to the TORC family.