Uracil misincorporation into DNA in cultured erythroblasts. Control (A) or folate-deficient (B) erythroblasts were cultured in folate-deficient (□) or control medium (▪). DNA was extracted from cells collected at various times. The uracils were removed from the DNA with uracil-DNA glycosylase, derivatized with 3,5-bis(trifluoromethyl)benzyl bromide, analyzed by gas chromatography-mass spectrometry, and expressed per 10⁶ thymines in the DNA sample. Results are the means ± 1 SEM of 7 to 17 separate samples. *P < .05 in steady-state levels of uracil in DNA in folate-deficient erythroblasts cultured in folate-deficient as compared with control medium.