cells were fixed for 10min in 1.8% of formaldehyde at 23 °C, nuclei were isolated, chromatin was fragmented by sonication (Covaris), The lysate was clarified by centrifugation before immunoprecipitation, and eluted by reverse crosslinking at 65deg for 14h. After RNaseA and ProteinaseK treatment, the DNA from Input and Immunoprecipitation was purified using AMPure XP Beads (Beckman Coulter); for Rpb3 ChIP experiments Drosophila Virilis chromatin was added prior to IP as spike control. For Biotin ChIP experiments exogenous Biotin-labeled DNA fragments were added prior to IP as spike control. NEB Next Ultra II