title: GSM8432602: ChIP_shScr_input_rep1; Mus musculus; ChIP-Seq
library_construction_protocol: Calibrated ChIP-seq was performed as described previously with minor modifications (Kriz et al., 2021). Briefly, MEF cells were trypsinized, resuspended in 1 million cells/mL of media and mixed with 50,000 HEK293 cells per 5 million mouse cells. Cells were crosslinked with 1% formaldehyde for 10 min at room temperature with rotation, and quenched with 0.2 M glycine for 5 min. Crosslinked cells were washed once with cold PBS, pelleted, and snap frozen in an EtOH/dry ice bath. Cell pellets were stored at -80C until further processing. 5-10 million cross-linked cells per IP were thawed on ice and resuspended in 300ul Lysis Buffer 1 (25mM HEPES pH 7.2-7.5, 25mM EDTA, 0.5% SDS). Nuclei were sonicated (Qsonica Q800 Sonicator) in polystyrene tubes at 40% power setting, 30s ON/30s OFF for a total sonication (ON) time of 6 min. After sonication, 1.2 mL of Lysis Buffer 2 (25mM HEPES pH 7.2-7.5, 187.5mM NaCl, 1.25% Triton X-100, 0.625% Na-deoxycholate, 6.25% glycerol, 1x cOmplete EDTA-free protease inhibitor cocktail) was added. 30ul of Dynabeads Protein G (Thermo Fisher Scientific) per IP were washed 3 times with ChIP Wash Buffer 1 (25mM HEPES pH 7.2-7.5, 150mM NaCl, 5mM EDTA, 1% Triton X-100, 0.5% Na-deoxycholate, 5% glycerol, 1x cOmplete EDTA-free protease inhibitor cocktail) and resuspended in 60ul ChIP Wash Buffer 1. Each IP was blocked with 20ul washed beads for 2 hours at 4C with rotation. The other 40ul of washed beads were incubated with antibody (5ul of RAD21 antibody or 2ul of H3K27me3 antibody/IP) for 2 hours at 4C. 5% input was taken from blocked lysates. Beads conjugated to antibody were added to blocked lysates and IP allowed to proceed overnight at 4C with rotation. IPs were then washed 3 times with cold ChIP Wash Buffer 1, 3 times with cold ChIP Wash Buffer 2 (25mM HEPES pH 7.2-7.5, 300mM NaCl, 5mM EDTA, 1% Triton X-100, 0.5% Na-deoxycholate, 5% glycerol, 1x cOmplete EDTA-free protease inhibitor cocktail). And 1 time with cold TENG (50mM Tris-HCl pH 8, 1mM EDTA, 50mM NaCl, 5% glycerol, 1x cOmplete EDTA-free protease inhibitor cocktail). All washes were performed by inverting tubes and setting aside for ~2 minutes per wash. IPs were then resuspended in 500ul TENG with 100ug RNAse A (Thermo Fisher Scientific) and incubated for 30 min at 37C. IPs were then washed 2 times with cold ChIP Wash Buffer 2 and 2 times with cold TENG without protease inhibitors. IPs were resuspended in 200ul elution buffer (50mM Tris-HCl pH 7.5, 10mM EDTA, 1% SDS) and incubated 15 min at 65C. Eluate was then transferred to a new tube and 198ul TE buffer (Ambion) and 40ug Proteinase K (Sigma) added. Inputs were thawed, TE buffer added to equalize volume to IPs and 200ul elution buffer and 40ug Proteinase K added. Inputs and IPs were then incubated for 2h at 45C and crosslinks reversed overnight at 65C. DNA was purified with phenol-chloroform extraction and resuspended in 50ul TE. Efficiency of ChIP was assayed via qPCR, with samples displaying over 10-fold enrichment of positive regions over negative control prepared for sequencing.  Experiments were performed in two biological replicates. Libraries were prepared from ~500ng of input or IP DNA using the NEBNext® Ultra II DNA Library Prep Kit for Illumina® (NEB) according to kit instructions.