Transcriptional coactivator for CREB1 which activates transcription through both consensus and variant cAMP response element (CRE) sites (PubMed:29211348). Acts as a coactivator, in the SIK/TORC signaling pathway, being active when dephosphorylated (PubMed:29211348). Acts independently of CREB1 'Ser-133' 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 PGC1alpha and inducer of mitochondrial biogenesis in muscle cells (By similarity). In the hippocampus, involved in late-phase long-term potentiation (L-LTP) maintenance at the Schaffer collateral-CA1 synapses. May be required for dendritic growth of developing cortical neurons. In concert with SIK1, regulates the light-induced entrainment of the circadian clock. In response to light stimulus, coactivates the CREB-mediated transcription of PER1 which plays an important role in the photic entrainment of the circadian clock. Binds, as a tetramer, through its N-terminal region, with the bZIP domain of CREB1 (By similarity). 'Arg-314' in the bZIP domain of CREB1 is essential for this interaction (By similarity). Interaction, via its C-terminal, with TAF4, enhances recruitment of TAF4 to CREB1 (By similarity). Interacts with 14-3-3 proteins, including YWHAE/14-3-3 epsilon (PubMed:28235073, PubMed:30611118). Interacts with calmodulin-dependent catalytic subunit PPP3CA/calcineurin A (PubMed:30611118). Cytoplasmic when phosphorylated by SIK or AMPK and when sequestered by 14-3-3 proteins (By similarity). Translocated to the nucleus on Ser-151 dephosphorylation, instigated by a number of factors including calcium ion and cAMP levels (By similarity). Light stimulation triggers a nuclear accumulation in the suprachiasmatic nucleus (SCN) of the brain (PubMed:23699513). Highly expressed in specific regions of the brain including the cortex, hippocampus and striatum. Expressed in a circadian manner in the suprachiasmatic nucleus (SCN) of the brain. Expression is highest during the day and reaches a nadir during the early subjective night. Phosphorylation/dephosphorylation states of Ser-151 are required for regulating transduction of CREB activity. TORCs are inactive when phosphorylated, and active when dephosphorylated at this site. This primary site of phosphorylation is mediated by SIKs (SIK1 and SIK2), is regulated by cAMP and calcium levels and is dependent on the phosphorylation of SIKs by LKB1. Belongs to the TORC family. Extended N-terminus.