library_construction_protocol: The collected cells were treated with 0.5 mg/mL proteinase K (Promega) in lysis buffer (50 mM Tris–HCl, pH 8.0, 50 mM EDTA, and 1% SDS) at 55 °C overnight. Subsequently, the lysates were treated with 300 µg/mL RNase A (Nacalai Tesque) at 37 °C for 30 min. Genomic DNAs were then extracted using the phenol-chloroform extraction method and precipitated with ethanol. The integrated lentivirus genome encoding sgRNA was amplified by PCR using Q5 Hot Start High-Fidelity 2X Master Mix (NEB). The P5 and P7 primers were designed according to the manufacturer's protocol (addgene #73179). The PCR cycling condition included an initial 1 min at 95 °C, followed by 30 s at 95 °C, 30 s at 53 °C and 30 s at 72 °C for 28 cycles, and a final 10 min extension at 72 °C. The PCR products were fractionated by electrophoresis using a 2 % agarose gel and subsequently purified using FastGen Gel/PCR Extraction Kit (NIPPON Genetic). The obtained products were further purified using AMPure XP beads (Beckman Coulter) to remove undesirable large fragments and remaining primers according to the manufacturer's protocol (addgene #73179). The quality of the sgRNA library was assessed by Tapestation using an HS D1000 Kit (Agilent).