ChIP experiments used about 20 million cells, using a protocol adapted from (Stock et al., 2007). For all ChIPs except those against EloB, cells were washed 2´ with PBS, and crosslinking was started by adding 1% formaldehyde in PBS to the plate, stopped by adding 0.125 M glycine, and cells were harvested by scraping and then pelleted. For ChIPs against EloB, cells were washed 2x with PBS, protein-protein crosslinking was performed with 40 ml ChIP Crosslink Gold (Diagenode, C01019027) or 2 mM DSP (ThermoFisher, cat 22586) in 10 ml PBS for 30 min, followed by two washes with PBS. Protein-DNA crosslinking (1% formaldehyde in PBS) was then performed on the plate for 10 min, stopped by 0.125 M glycine and cells were harvested by scraping and then pelleted. Cell pellets were resuspended and incubated for 10 min in 2 ml swelling buffer (25 mM HEPES [pH 7.9], 1.5 mM MgCl2, 10 mM KCl, 0.1% NP40, protein and phosphatase inhibitors) and the suspension was homogeneized (tight pestle, 50x). Nuclei were pelleted (3,000 g, 5 min) and resuspended in 1.3 ml sonication buffer (50 mM HEPES [pH 7.9], 140 mM Nacl, 1 mM EDTA, 1% Triton X-100, 0.1% Na-deoxycholate, 0.1% SDS, protease and phosphatase inhibitors). Sonication (Diagenode Bioruptor, 30 s ON/30 s OFF, high potency, 2x 8 cycles with fresh ice in between). Insoluble material was pelleted, and chromatin concentration and sonication efficiency was determined in the supernatant by DNA quantification or agarose gel after decrosslinking the extracts overnight. ChIPs were performed O.N. using 20-30 μg of DNA, 4 μg antibody (the amount of antibody for reaching full enrichment was titrated) and 25 μl of protein A dynabeads in 500 μl of sonication buffer. ChIPs were washed once with sonication buffer, once with buffer wash buffer A (50 mM HEPES [pH 7.9], 500 mM Nacl, 1 mM EDTA, 1% Triton X-100, 0.1% Na-deoxycholate, 0.1% SDS, protease and phosphatase inhibitors), once with wash buffer B (20 mM Tris-Cl [pH 8.0], 250 mM LiCl, 1 mM EDTA, 0.5% Triton MP40, 0.5% Na-deoxycholate, protease and phosphatase inhibitors) twice with 1x TE pH 8.0 and eluted in 200 μl TE pH 8.0, 1% SDS followed by decrosslinking (O.N) and RNAse treatment. DNA was finally purified over PCR (Qiagen) and eluted in 55 μl water. Libraries were prepared according to Illumina instructions.