title: GSM8487814: HEK293, RPB1, Control, rep2; Homo sapiens; ChIP-Seq
library_construction_protocol: For RPB1 samples,  HEK293T cells expressing shControl or shRPRD1B cells were crosslinked by 1% formaldehyde for 10 min. Crosslinking was quenched with 0.125 M glycine for 5 min. Cells were successively lysed in lysis buffer LB1 (50 mM HEPES-KOH, pH 7.5, 140 mM NaCl, 1 mM EDTA, 10% glycerol, 0.5% NP-40, 0.25% Triton X-100, 1× PI), LB2 (10 mM Tris-HCl, pH 8.0, 200 mM NaCl, 1 mM EDTA, 0.5 mM EGTA, 1× PI) and LB3 (10 mM Tris-HCl, pH 8.0, 100 mM NaCl, 1 mM EDTA, 0.5 mM EGTA, 0.1% Na-deoxycholate, 0.5% N-lauroylsarcosine, 1× PI). Chromatin was sonicated to an average size of ~200–500 bp using UCD-200 Biorupter (30s on and 30 s off for 30 min). A total of 5 μg of RPB1 antibody (cat: ab76123) was pre-mixed in a 50μl volume of Dynabeads protein A (Invitrogen) and was added to each sonicated chromatin sample and incubated overnight at 4°C. The chromatin-bound beads were washed two times with low salt buffer (0.1% Na Deoxycholate, 1% Triton X-100, 1mM EDTA, 50mM HEPES pH 7.5, 150mM NaCl), once with high salt wash buffer (0.1% Na Deoxycholate, 1% Triton X-100, 1mM EDTA, 50mM HEPES pH 7.5, 500mM NaCl), once with LiCl wash buffer (250mM LiCl, 0.5% NP-40, 0.5% Na-Deoxycholate, 1mM EDTA, 10mM Tris-Cl pH 8.0) and twice in TE buffer. The chromatin was reverse crosslinked overnight at 65°C with shaking at 750rpm. After DNA extraction using phenol-chloroform, the DNA was resuspended in 10mM Tris-HCl pH 8.0. The purified DNA was subjected to qPCR to confirm target region enrichment before moving on to deep sequencing library preparation. For sequencing, the extracted DNA was used to construct the ChIP-seq library using the NEBNext Ultra II DNA Library Prep Kit followed by sequencing with an Illumina NovaSeq X Plus system.