Acetylates histones, giving a specific tag for transcriptional activation. Also acetylates non-histone proteins, like DDX21, FBL, IRF2, MAFG, NCOA3, POLR1E/PAF53 and FOXO1. Binds specifically to phosphorylated CREB and enhances its transcriptional activity toward cAMP-responsive genes. Acts as a coactivator of ALX1. Acts as a circadian transcriptional coactivator which enhances the activity of the circadian transcriptional activators: NPAS2-ARNTL/BMAL1 and CLOCK-ARNTL/BMAL1 heterodimers. Acetylates PCNA; acetylation promotes removal of chromatin-bound PCNA and its degradation during nucleotide excision repair (NER). Acetylates POLR1E/PAF53, leading to decreased association of RNA polymerase I with the rDNA promoter region and coding region . Acetylates DDX21, thereby inhibiting DDX21 helicase activity. Acetylates FBL, preventing methylation of 'Gln-105' of histone H2A (H2AQ104me). Functions as a transcriptional coactivator for SMAD4 in the TGF-beta signaling pathway.