Bivalent Pc2TF shows cooperative and on-target binding with H3K27me3 ligands. (A) The scatter plot shows mean HRP signal at an absorbance of 450 nm (one ELISA trial, means of four technical replicate wells, error bars = SDM) from wells in which 0.1 μM purified protein (Pc2TF, PcTF, or PcΔTF) was allowed to bind with different proportions of H3K27me3 biotinylated peptides (0–100%) mixed with unmodified H3 and tethered to neutravidin-coated surfaces. (B) Hill curves were fit to data for three ELISA trials (dots = technical replicate wells from all trials). (C) ELISA was used to detect interaction of 0.05 μM purified proteins with immobilized histone H3 peptides that were trimethylated at lysine 27, 4, or 9 or unmodified. The bar chart shows mean signal values from anti-mCherry-HRP at an absorbance of 450 nm (4 technical replicates, bars = SDM).