Lentivirus production and infection were performed as previously described21 (link). Briefly, HEK293T cells were transfected with third generation packaging plasmids and individual sgRNA vectors or CDKO libraries. Lentivirus was harvested after 48 h and 72 h and filtered through a 0.45 μm PVDF filter (Millipore). Spin infections were used to deliver sgRNA vectors and libraries into K562 cells.