E1A-like inhibitor of differentiation-1 (EID-1), an acetyltransferase enzyme, binds both the retinoblastoma protein (Rb), a regulator of cell cycle and tissue specific transcription, and the adenovirus E1A-associated cellular p300 transcriptional co-activator protein. EID-1 inhibits cellular differentiation by blocking the histone acetyltransferase activity of p300. EID-1 also acetylates both histones and non-histone proteins such as NCOA3 co-activator. By acetylating histones, EID-1 gives a specific tag for transcriptional activation. In addition to binding Rb and p300, EID-1 also binds to phosphorylated CREB protein, mediating cAMP gene regulation. EID-1 augments the activity of phosphorylated CREB and activates transcription of cAMP responsive genes as a co-activator.