CTBP1 is a protein that binds to the C-terminus of adenovirus E1A proteins. CTBP1 is a cellular phosphoprotein that associates with various proteins and functions as a corepressor of transcription.This protein and the product of a second closely related gene, CTBP2, can dimerize. CtBP1 is expressed from embryo to adult, but CtBP2 is mainly expressed during embryogenesis.