SMG9 and chronic myelogenous leukemia, BCR-ABL1 positive: ATRi resistance within the context of SMG8 or SMG9 deficiency was not unique to the YCC6 cells; SMG8 or SMG9 mutant HAP1 cells (chronic myelogenous leukemia cells with homozygous premature truncating mutations and loss of WT protein; Supplementary Fig. S2E–S2H) were also resistant to ATRi (Fig. 2J; Supplementary Fig. S2I).