Cells (20 million per ChIP reaction for all but EWS/FLI1, which required 40 million cells) were crosslinked with warm 1% methanol-free formaldehyde (ThermoFisher) for 10 minutes at room temperature rotating at 12 RPM. The reaction was quenched by adding glycine to a final concentration of 0.125M and incubating for an additional 5 minutes at room temperature rotating at 12 RPM. Cell pellets were washed three times with ice cold PBS and resuspended in 1 ml of SDS lysis buffer (1% SDS, 10 mM EDTA, 50 mM Tris-HCl pH8) supplemented with protease inhibitor cocktail including phenylmethylsulfonyl fluoride (PMSF) and incubated at RT for 2 minutes with gentle rotation. Lysates were centrifuges at 15,000 G for 10 minutes at 4°C and the pellet was re-suspended in 900 µl of ChIP IP buffer (2:1 SDS lysis buffer : triton dilution buffer), transferred to milliTUBE (covaris). Sonication was performed on a E220 Focus Ultra Sonicator (Covaris) using the setting (duty cycle 5%, peak power 140W, cycles per burst 200, Temperature 4°C, time 30 minutes/millitube). ChIP inputs from sheared chromatin were de-crosslinked by adding de-crosslinking buffer (NaHCO3, NaCl, RNase A, Proteinase K) and incubating for two hours at 65°C in a thermal cycler. The remaining sheared chromatin was incubated with primary antibody coupled to Protein A DynaBead (Beckman Coulter, antibody bead conjugation was performed for 16 hours) overnight, rotating at 4°C. As a calibration control, antibody against a drosophila specific histone variant H2Av and drosophila chromatin (active motif) were used as per the recommendation of the manufacturer. The next day, ChIP product was eluted from the Dynabeads in 100 µl of elusion buffer and de-crosslinked for 12 hours at 65°C. For both Input and chipped material, AMPure XP beads (Beckman coulter) were used to purify DNA. Chromatin immunoprecipitation sequencing for EWS/FLI1, SMC1A, STAG1, STAG2, H3K27me3: ChIP-seq libraries were prepared using Swift S2 Acel reagents on a Beckman Coulter Biomek i7 liquid handling platform from approximately 1 ng of DNA according to the manufacturer's protocol and 14 cycles of PCR amplification. Finished sequencing libraries were quantified by a Qubit fluorometer and samples were QC'D using a Bioanalyzer Tapestation (Agilent Technologies 2200) to determine fragment size. Library pooling and indexing was evaluated with shallow sequencing on an Illumina MiSeq. Subsequently, libraries were sequenced on a NovaSeq targeting 40 million 100bp read pairs by the Molecular Biology Core facilities at Dana-Farber Cancer Institute. Chromatin immunoprecipitation sequencing for H3K27ac: Chromatin was sheared to about 200 bp fragments using the Covaris ultra-sonication. The lysate was diluted with ChIP dilution buffer (16.7 mM Tris-HCl pH 8.1, 16.7 mM NaCl, 1.2 mM EDTA, 1.1% Triton-X100, 0.01% SDS) and cleared by centrifugation. 5% of the supernatant volume set aside as an input control. The remaining lysate was incubated over night at 4°C with 5 ug of antibody (3 ug for histone antibodies).