CDKN2A and melanoma: We designed a nucleotide-focused sgRNA library targeting 128 genes directly involved in nucleotide biosynthesis, salvage, and catabolism (referred to as the “nucleotide metabolism signature”; Supplementary Table S1), and performed a dropout screen in SKMEL28 human melanoma cells with wildtype p16 and p16 knockdown (Fig. 1A; Supplementary Fig. S1A).