Fig. 7. Quantification of HP1 binding and competition experiments. (A) Concentration dependence of GST–mHP1a, GST–M31 and GST–M32 binding to urea-extracted nuclear envelopes. Metabolically labeled probes (signified by asterisks) were prepared as explained in Materials and methods. Background binding to proteolyzed membranes has been subtracted. (B and C) Competition experiments using radiolabeled probes (∼1 µM) and excess unlabeled HP1 proteins as indicated. All experiments shown here were done in triplicate. Variation between data points did not exceed 10%.