Nbs1-S343A mutant decreases MMC resistance in CML-BC cells. CD34⁺ NBMC and CML-BC cells were infected with pMig retroviral particles containing Nbs1-wt, Nbs1-S343A, or empty plasmid. (A) pNbs1 was examined by immunofluorescence after 0.1 μg/mL MMC treatment for 24 hours. Expression of GFP and detection of pNbs1 foci is shown in representative nuclei. (B) Survival of GFP⁺ cells 24 and 48 hours after MMC treatment was determined using trypan blue exclusion. Results represent mean (± SD) for 2 donors each for NBMC and CML-BC. *P < .04, CML-BC-GFP Nbs1-S343A in comparison to CML-BC-GFP empty and CML-BC-GFP Nbs1-wt, and NBMC-GFP-Nbs1-S343A in comparison to NBMC-GFP empty and NBMC-GFP Nbs1-wt; **P < .02, CML-BC-GFP Nbs1-S343A in comparison to CML-BC-GFP empty and CML-BC-GFP Nbs1-wt.