Genomic DNA was extracted from collected cell pellets using a Zymo Quick DNA miniprep kit (#D3024). The sgRNA were PCR amplified by NEBNext Ultra II Q5 Master Mix (NEB #M0544) from the genomic DNA using the indexed PCR primers with next-generation sequencing adapters compatible with Illumina's NEXTERA kit. PCR products were size-selected by gel electrophoresis, quantified byQubit(Thermo Fisher Scientific) and sequenced using HiSeq (Illumina). CRISPR Screening