Journal: Genome Research
Article Title: RNA-DNA hybrid (R-loop) immunoprecipitation mapping: an analytical workflow to evaluate inherent biases
Figure Lengend Snippet: Experimental design: constructing DRIP schemes. ( A ) Experiments 1–16 explore the effect of formaldehyde-fixation (Step 1), nucleic acid isolation (Step 2), removal of free RNA (Step 3), and nucleic acid fragmentation (Step 4) on the outcome of RNA-DNA hybrid detection. Each experiment was performed at two parallel cell lysis temperatures (65°C and 37°C), respectively. The temperature variable is not depicted in the cartoon, but it is referred in the main text. ( B ) Experiments 17–24 test the impact of acoustic sharing performed on a chromatin prep rather than on naked nucleic acid, similarly to the ChIP protocol. Each experiment was performed at 65°C cell lysis temperature. ( C ) Workflow of a ChIP experiment (shown only for comparison with the DRIP pipeline). (HCHO) Formaldehyde fixation, (Phe/Chl) phenol-chloroform extraction, (Kit) silica membrane-based nucleic acid purification, (RNase A) Ribonuclease A digestion performed at high (300 mM) NaCl concentration, (Son) sonication, (RE) restriction enzyme cocktail digestion (HindIII, EcoRI, BsrGI, XbaI, and SspI). As a negative control, RNase H digestion was applied in all DRIP experiments (not indicated in the cartoon).
Article Snippet: 2, 4, 6, 8, 10, 12, 14, and 16, purified DNA samples (∼25 µg each) were fragmented using a restriction enzyme cocktail of 1 µL HindIII (20 U/µL), 1 µL EcoRI (20 U/µL), 2 µL BsrGI (10 U/µL), 1 µL XbaI (20 U/µL), and 4 µL SspI (5 U/µL) in NEB Buffer 2 (NEB) (V = 300 µL) at 37°C for 4 h. The fragmented DNA samples were repurified either by phenol-chloroform extraction (experiments 1–4, 9–12) or by the NucleoSpin Gel and PCR Clean-up kit (Macherey-Nagel) (experiments 5–8, 13–16).
Techniques: Isolation, Lysis, Chromatin Immunoprecipitation, Nucleic Acid Purification, Concentration Assay, Sonication, Negative Control