TK1 inactivation causes only minor RS in hematopoietic cells. (A) dTTP and dCTP pools from WT (black bars) and TK1^−/− (gray bars) DN Thymocytes, BM-resident B cell progenitors, and BM-resident erythroid progenitors. Data are mean values ±SEM for three independent measurements. n = 4 mice/genotype/replicate; *, P < 0.005; **, P = 0.0001. (B) Concentrations (fmol per 10⁶ cells) of [¹³C/¹⁵N]-dCTP (black bars) and [¹³C/¹⁵N]-dTTP pools (gray bars) from WT and TK1^−/−-nucleated BM cells and DN thymocytes. Data are means ±SEM from n = 5 (WT) and n = 4 (TK1^−/−) mice from two independent experiments. (C) Western blot detection of pChk1 in lysates from lymphoid and erythroid progenitors. Total CHK1 protein was used as a loading control. (D) Representative example of total DNA content staining in EryA cells from WT and TK1^−/− cells, and (E) quantification of percentage of DN3b thymocytes, Hardy B-C cell, and EryA cells in S-phase as determined by total DNA content staining. Data are mean values ±SEM. n = 3 mice/genotype. (F) Representative example of pH2A.X detection in WT and TK1^−/− EryA cells. (G) Quantification of pH2A.X-positive staining in DN3b thymocytes, Hardy B-C cell, EryA cells from WT (black bars), and TK1^−/− (gray bars) mice. n = 4 mice/genotype. NS, P > 0.05; *, P < 0.03.