[3H]Thymidine incorporation into TM6 cells after Se-methylselenocysteine (MSC) treatment. (a) Asynchronous TM6 cells were grown for 24 hours and treated with various concentrations of MSC for 48 hours to determine the optimum dose for treating synchronized cells. (b) Synchronized TM6 cells were treated with 50 μM MSC at 6 hours and the DNA synthesis was measured by [3H]thymidine incorporation at the indicated time points as described in the Materials and methods section. Data are presented as means ± SEM for three observations at each given time point. MSC at 50 μM showed a greater ability to block DNA synthesis in asynchronous TM6 cells, mainly because of the extended time of treatment.