Each sample was washed twice with ice-cold phosphate-buffered saline and then lysed in lysis buffer (25 mM Hepes pH 7.9, 1.5 mM MgCl2, 10 mM KCl, 0.1% NP-40, freshly added protease inhibitor from Sigma, St Louis, MO, USA), homogenized on ice and spun at 3000 g for 5 min at 4 °C. The pellet was re-suspended in sonication buffer (50 mM Hepes, 140 mM NaCl, 1 mM EDTA, 1% Triton X-100, 0.1% Na-deoxycholate, 0.1% SDS, freshly added protease inhibitors) and sonicated for at least 20 min. The sample was then spun down for 10 min at 4 °C. The chromatin containing supernatant was stored at −80 °C until immunoprecipitation. End-repair of DNA, adding 'A' bases to the DNA, ligation of sequencing adaptors to DNA fragments and amplification of adaptor modified DNA by PCR was done according to the recommended Illumina protocol. For gel purification of the 'SolexaPreGel for ChIPSeq' a 2% agarose Tris-acetate-EDTA gel was loaded with the entire sample using loading buffer containing Xylene cyanol (Sigma, X4126). Band fragments of 200–300 bp were excised using a Dark Reader and DNA was purified with the Qiagen MinElute Gel Extraction Kit (Qiagen, West Sussex, UK). DNA was eluted with 15 μl EB preheated to 50 °C.