Antibodies recognising H3K122ac and H3K64ac were previously described7 (link),9 (link). mESCs were cross-linked in 1% formaldehyde for 10 min and then quenched by the addition of glycine to a final concentration of 0.125 M. Chromatin was sheared using a biorupter (Diagenode) to an average fragment length of ~100 – 200bp. Sequential ChIP was performed as described previously32 (link). Briefly, 5 µg antibodies against H3K4me3 (07-473, Millipore) and H3K27me3 (07-449, Millipore) were covalently coupled to Dynabeads using Invitrogen antibody coupling kit (Cat. 14311D) according to the manufacturer’s instructions. The first ChIP was performed using either H3K4me3 or H4K27me3 antibodies, and the immunoprecipitated chromatin was then eluted with 10 mM DTT, diluted 30 times with RIPA buffer (1X PBS, 1% NP-40, 0.5% Sodium Deoxycholate, 0.1% SDS, *Roche Protease Inhibitor Cocktail) before performing the second ChIP with anti-H3K122ac9 (link). Purified chromatin was quantified by qPCR using the standard curve method and expressed as % of input bound. Primer details are given in Supplementary Table 2.