MLLT3 and leukemia: First, we performed a high-density CRISPR gene tiling scan (15–21) in MLL-AF9-Cas9+ leukemia using a pool of 147 sgRNAs that targeted every “NGG” protospacer adjacent motifs (PAMs) within the endogenous Sgf29 coding exons (Fig. 5A and data S7 and S8; targeting density of ~2.0 amino acids/sgRNA).