GSE183083
Genome wide mapping of DDX41 chromatin binding using a targeted nuclease approach in U2OS cells after expression
Purpose: Investigation of DDX41 chromatin binding sites in U2OS cells Method: Expression of DDX41-GFP was induced for 48 hours before crosslinking using 1µg/ml docycycline. Control cells were not induced with doxycline. Cells were mildly crosslinked using 1% FA for 2 min at RT. Concanavalin A-coated beads were activated in Binding Buffer (20 mM Hepes-KOH pH 7.9, 10 mM KCl, 1mM CaCl2, 1 mM MnCl2).1*10^6  U2OS cells were washed twice with Wash Buffer (Hepes-NaOH pH7.5, 150 mM NaCl, 0.5 mM Spermidine, 1 mM protease inhibitor) at room temperature and afterwards immobilized on the activated beads in 1 ml Wash Buffer. Cells were permeabilized with 0.05% digitonin in Wash buffer for 4 min at RT. 1 µg Nanobody-GFP-MNase (in-house protein production, PMID:25362362) binding was performed at 4°C for 30 min in 0.05% digitonin-Wash buffer. After 2x washing, the MNase was activated by adding 3mM CaCl2 on ice for 30 min.  2x Stop Buffer (68 µl 5M NaCl, 40 µl 0.5 M EDTA, 20 µl 0.2 M EGTA, 10 µl 5% digitonin, 5 µl 10mg/ml RnaseA, )) was mixed with the samples to stop the reaction. Chromatin fragments were released by incubating the samples for 20 minutes at 37°C and centrifugation at 16.000×g for 10 minutes at 4°C. Supernatants were incubated at 70°C in the presence of 0.1% SDS and 5 µg proteinase K. Before library preparation, the DNA was recovered by phenol-chloroform extraction Results: We succesfully mapped DDX41 binding sites on cromatin in U2OS cells. DDX41 preferentially binds in the promoter region of genes. Overall design: U2OS cells that dox-inducible express GFP-tagged DDX41 protein were either induced or not with 1 µg/ml doxycycline for 48h. Control cells did not express GFP-tagged DDX41. Cells were mildly crosslinked. Nanobody-GFP-Mnase was use to perform  CUT&RUN.