DNA was cross-linked for 10 minutes with 1% formaldehyde and stopped in 0.125 M glycine. Purified chromatin was sonicated to ~250 bp using the Bioruptor (Diagenode, Inc) and incubated with the IgG or Histone H3 (tri methyl K4) as previously described in http://farnham.genomecenter.ucdavis.edu/pdf/FarnhamLabChIP%20Protocol.pdf.