ChIP was performed as described in Jakobsen et al, BMC genomics, 16, 46 (2015) Amplification of 2 ng ChIP DNA was essentially performed as described by the manufacturer (NEB, cat#E6240S), with the use of precast 2% SYBR agarose gels (Invitrogen, cat#G5218-02) and excision of band size 175–400 bp. Key modifications consisted of a 30 minute ligation step, 30 minute gel solubilization at 37°C of excised gel fragments, and a prolonged, double run-through elution step (each three minutes) with preheated (55°C) elution buffer for all column purifications (Qiagen, cats#28104,28704,28004) to ensure robust recovery.