ChIP experiments of Ty1-tagged Mod(mdg4) isoforms are performed by truChIP Chromatin Shearing Kit according to manufactures instruction with minor modifications. 2x107 OSC were fixed with 1% formaldehyde 10min and quenched and lysed with buffers of truChIP Chromatin Shearing Kit. Fixed chromatin is sheered with Bioruptor II (BMbio BR2012A) for 20 cycles of 30s ON/30s OFF, high settings. Sheered chromatin is immunoprecipitated by antibody-conjugated Dynabeads protein G for 2hr. Immunoprecipitated chromatin was incubated with Proteinase K and RNase, and de-crosslinked at 65°C overnight. For ChIP experiments of RNA polymerase II, 2x107 OSC were fixed with 1% formaldehyde 10min and quenched with final 0.1M Glycine for 5min. After twice wash with PBS, nuclei were isolated with 1ml of swelling buffer (25mM HEPES-KOH(pH 7.5), 1.5mM MgCl2, 10mM KCl, 0.1% NP-40, 1mM DTT and 1x Protease Inhibitor). Isolated nuclei were lysed in 400µl of sonication buffer(50mM HEPES-KOH(pH 7.4), 140mM NaCl, 1mM EDTA, 1% Triton X-100, 0.1% Na-deoxycholate, 0.1% SDS and 1xProtease Inhibitor) and were sheered with Bioruptor II (BMbio BR2012A) for 20 cycles of 30s ON/30s OFF, high settings. 3µg of antibody were incubated with chromatin for overnight. Next day, 20µl of Dynabeads M-280 Sheep anti-Mouse IgG is added to sample and incubated for 1hr. Beads were washed and treated with Proteinase K and RNase as described (Haring et al., 2007). DNA was purified with isopropanol precipitation using Pellet Paint NF Co-precipitant (Merck: 70748). Fragments from the ChIP experiment were sheared to ∼200 bases using Covaris S220. These were used for library preparation with the NEBNext Ultra II DNA Library Prep Kit for Illumina (NEB) following the manufacturer's protocol.