library_construction_protocol: 200-300 ng of cellular small RNA (size < 200 nt) was fragmented into 40-50 nt under alkaline condition(5 ul NaHCO3 buffer pH=9.2) and purified by Oligo Clean & Concentrator. Then RNA was subjected to demethylation treatment with 1.0 µL of engineered AlkB (D135S, 10 mg/mL) with the reported recipe, followed by purification using Oligo Clean & Concentrator. Chromatin associated RNA purified from cells was added RNase free water to 45 ul and 5 ul NaHCO3 buffer (pH = 9.2) was added and the mixture was incubated at 95 °C for 10 min and then transferred into ice. It was purified by Oligo Clean & Concentrator. Libraries were prepared according to Illumina's instructions.