FAC gene replacement normalizes the cell cycle response of FA(C) lymphoblasts to low-dose MMC. Cells were treated with control medium or medium containing 40 ng/mL MMC for 2 hours. Following treatment, the cells were washed three times and placed back in culture in complete medium. After 24 hours the cells were obtained and DNA content measured by PI staining and flow cytometry. Results of a representative experiment are shown. The shaded area represents cells in S phase.