Thermodynamic parameters of HP1:H3K9me3 binding measured by isothermal titration calorimetry.

Proteina	K d (μM)	ΔH° (kcal mol−1)	−TΔS° (kcal mol−1)
HP1 wild type	15 ± 2	−5.8 ± 0.3	−0.9 ± 0.3
HP1–Y24W	14 ± 3	−10.6 ± 0.7	4.0 ± 0.8
HP1–Y48W	23 ± 3	−10.4 ± 0.6	4.1 ± 0.6
HP1–Y24W/Y48W	55 ± 16	−9 ± 2	3 ± 2

^aExperiments were performed by titrating H3K9me3 peptide (3–3.5 mM) into HP1 mutants (180–230 μM) in 50 mM sodium phosphate, pH 7.4, 150 mM NaCl, 2 mM TCEP at 25 °C. Values are average of three independent experiments, and calculated error is standard deviation of measurements.