P-GSE41187-1 - P-GSE41187-1
sample treatment protocol
Cell pellets (from initial 50 ml of culture) were thawed and resuspended in 250ul of IP buffer (100 mM Tris pH 8, 300 mM NaCl, 2% TritonX-100) and sonicated using a microtip sonicator set at 10% output for 20 second intervals with periods of cooling in between. Cells were then treated for one hour at 4 °C with RNase A (2 ng/ml) micrococcal nuclease (50 units), 20 μM CaCl2,1.2 mM KCl, 0.3 mM NaCl, 6 mM sucrose, and 10 μM DTT. After treatment, a distribution of DNA fragments ranging from 200-600 bp was detected by agarose-gel electrophoretic separation of a small sample that was de-crosslinked by incubation at 65 °C for >4 hr. EDTA was added to 10 mM to stop the micrococcal nuclease and the samples were spun down to remove cell debris. The lysate was then incubated with a 50/50 slurry of Sepharose protein A beads and protein G beads in IP buffer for 2-3 hours at 4 °C. The beads were removed by centrifugation and antibody was added to the pre-cleared lysate for an overnight incubation. The next day, 30 μl of a 50/50 slurry of Sepharose protein A and G beads in IP buffer was added to the lysate to capture antibody-protein-DNA complex for one hour at 4 °C. Beads were then washed once with 1 ml of 250 mM LiCl wash buffer (100 mM Tris pH 8, 250 mM LiCl, 2% TritonX-100), twice with 600 mM NaCl wash buffer (100 mM Tris pH 8, 600 mM NaCl, 2%SDS), twice with 300 mM NaCl wash buffer (100 mM Tris pH 8, 300 mM NaCl, 2%SDS), and twice with TE. Elution buffer (50 mM Tris pH 8, 10 mM EDTA, 1% SDS) was added after the final wash step, and beads were incubated at 65 °C for 30 minutes toremove the crosslinked protein-DNA complexes from the beads. After centrifugation to remove the beads, the samples were incubated overnight at 65 °C to reverse the protein-DNA formaldehyde crosslinks. DNA was purified using Qiagen’s PCR Purification kit and eluted to a final volume of 50ul with EB.