Amyloid-β precursor protein (APP), a widely expressed cell-surface protein, is cleaved in the transmembrane region by γ-secretase. γ-Cleavage of APP produces the extracellular amyloid β-peptide of Alzheimer's disease and releases an intracellular tail fragment of unknown physiological function. We now demonstrate that the cytoplasmic tail of APP forms a multimeric complex with the nuclear adaptor protein Fe65 and the histone acetyltransferase Tip60. This complex potently stimulates transcription via heterologous Gal4- or LexA-DNA binding domains, suggesting that release of the cytoplasmic tail of APP by γ-cleavage may function in gene expression.