ALKBH3 CLIP-seq in HeLa cells.

The CLIP procedures were conducted using HeLa cells according to the previous study (Liu et al., 2016) with slight modifications. Briefly, 4 plates of HeLa cells in 15 cm dishes were transfected with pPB/ALKBH3 plasmid for 48 h to reach about 90% cell confluency. After washing twice with ice-cold PBS, cells were irradiated twice with 400 mJ/cm2 at 254 nm by Stratalinker on ice. Cells were lysed in high salt lysis buffer (300 mM NaCl, 0.2% NP-40, 20 mM Tris-HCl PH 7.6, 0.5 mM DTT, protease inhibitor cocktail (1 tablet/50 ml), and RNase inhibitor (1:200)) at 4°C for 30 min. Supernatant was collected after centrifuged at 17,000 g at 4°C for 15 min and further treated with 1 U RNase T1 for 15 min at 24 °C. After centrifugation and filtration through 0.22 µM filter, 10% supernatant was collected as input for further sequencing analysis. Anti-Flag M2 beads (Sigma-Aldrich, St. Louis, MO, 80 µl) were washed three times with lysis buffer and incubated with the filtered supernatant at 4°C for 4 hrs. After removing the flow through by magnetic rack, beads and input were further incubated with 10 U RNase T1 exactly for 8 min. Samples were treated with 95 µL commercial PNK buffer and 0.5 U PNK for 15 min at 37 °C. After treatments, final concentration of 100 µM ATP and 1 U PNK were added and incubated at 37 °C for another 30 min. The RNA/protein complexes were eluted by NuPAGE 1 × loading buffer and fractionated by neutral NuPAGE 4–12% bis-tris gel. After cutting the gel, RNAs were recovered by proteinase K digestion in proteinase K buffer, followed by phenol/chloroform extraction using glycogen as carrier. The RNA fragments were ligated to adapter and established library by NEB small RNA library preparation kit (E7330S). Overall design: Examination of RNAs bound by ALKBH3 in HeLa cells