Procedures were adapted from Reyes et al. (32) . Highsalt method: isolated nuclei were resuspended in 1 ml of CSK buffer (10 mM PIPES pH 6.8, 100 mM NaCl, 300 mM surcose, 3 mM MgCl 2 1 mM EGTA, 1 mM DTT, 1 mM PMSF, 0.5% TritonX-100 with protease inhibitor cocktail [Roche]-one tablet per 50 ml), incubated for 3 min at 48C and spun down at 5000g for 3 min to separate nuclei from soluble proteins. Next the chromatin was solubilized by RNase-free DNase I digestion (0.1 mg, Warthington) in 1 ml of CSK buffer for 15 min at 378C. Next, ammonium sulfate was added to a final concentration of 0.25 M and after a short incubation (5 min at 48C) the samples were centrifugated again. The resulting pellet was extracted three times with 2 M NaCl in CSK buffer in the following steps: resuspension, incubation at 48C for 5 min and centrifugation. 