Acetylates histones; giving a specific tag for transcriptional activation. Also acetylates non-histone proteins; like NCOA3 and FOXO1. Binds specifically to phosphorylated CREB and enhances its transcriptional activity toward cAMP-responsive genes. Acts as a coactivator of ALX1 in the presence of EP300. Acts as a circadian transcriptional coactivator which enhances the activity of the circadian transcriptional activators: NPAS2- ARNTL/BMAL1 and CLOCK-ARNTL/BMAL1 heterodimers. {ECO:0000250|UniProtKB:Q92793}.