Quantitative liquid β-galactosidase assays were performed on at least three independent colonies for each combination. The numbers represent the fold activation above background. The background is defined as the amount of β-galactosidase activity detected in the yeast, with cotransformation of corresponding prey plasmids and the bait plasmid expressing APP intracellular domain–LexA fusion protein, which has the same level of β-galactosidase activity as the yeast containing the prey plasmid and the LexA bait vector plasmid without any cDNA insert.