GSM2870423: 3C-seq of E. coli wt cells in exponential phase LB 30°C -Replicate 1; Escherichia coli str. K-12 substr. MG1655; OTHER
For 3C-seq: ≈ 1-2 x 109 crosslinked cells (7% formaldehyde, unless otherwise stated ) are suspended in 600 μl Tris 10 mM EDTA 0.5 mM (TE) (pH 8) with 4 μl of lysozyme (35 U/μl; Tebu Bio), and incubated at RT for 20 minutes. SDS is added to the mix (final concentration 0.5%) and the cells are incubated for 10 minutes at RT. 50μl of lysed cells are then transferred in 8 tubes containing 450μL of digestion mix (1X NEB 1 buffer, 1% triton X-100, and 100U HpaII enzyme). DNA is digested for 3 hours at 37°C, split in 4 aliquots, and diluted in 8 ml ligation buffer (1X ligation buffer NEB without ATP, 1 mM ATP, 0.1 mg/ml BSA, 125 Units of T4 DNA ligase 5 U/μl). Ligation is then performed at 16°C for 4 hours, followed by incubation overnight (ON) at 65°C in presence of 250 μg/ml proteinase K and 5 mM EDTA. Precipitation of DNA is performed using an equal volume of 3 M Na-Acetate (pH 5.2) and two volumes of iso-propanol. After one hour at -80°C, DNA is pelleted, suspended in 500μl 1X TE buffer, and incubated for 30 minutes at 37°C in presence of RNAse A (0.03 mg/ml). DNA is then transferred into 2 ml centrifuge tubes, extracted twice with 500 μl phenol-chloroform pH 8.0, precipitated, washed with 1 ml cold ethanol 70% and diluted in 30 μl 1X TE buffer. All tubes are pooled and the resulting 3C library is quantified on gel using Quantity One software (BioRad). 3C-seq: 5 µg of a 3C library was suspended in water (final volume 130 µL) and sheared using a Covaris S220 instrument (Duty cycle 5, Intensity 5, cycles/burst 200, time 60 sec for 4 cycles). The DNA was purified and processed according to manufacturer instructions (Paired-End DNA sample Prep Kit – Illumina – PE-930-1001), except that DNA was ligated to custom-made adapters (see Marbouty M. et al, 2015, Mol Cell) for 4 hours at room temperature. Tubes were then incubated at 65°C for 20 minutes. DNA fragments ranging in size from 400 to 900 pb were purified using a PippinPrep apparatus (SAGE Science). For each library, four test PCR reactions were performed to determine the optimal number of PCR cycles (1 or 2 µL of the collected DNA, Illumina primers PE1.0 and PE2.0 using Taq Phusion [Finnzymes]). A large-scale PCR (8 reactions) was then set-up with the number of PCR cycles determined previously. The PCR product was finally purified on Qiagen MinElute columns and subject to paired-end sequenced on an Illumina sequencer.