Figure 4

MyoD^-/-myoblasts enter S-phase more readily than WT myoblasts. (A) Western blot was performed using the indicated antibodies and nuclear protein isolated from a differentiation time course of WT and MyoD^-/- primary myoblasts. (B) Cdk2 was immunoprecipitated from protein extracts of a differentiation time course of WT and MyoD^-/- primary myoblasts, and assayed for kinase activity using histone H1 and γ-³²P-ATP as substrate. (C) Proliferating WT and MyoD^-/- myoblasts were fixed in ethanol and DNA stained with propidium iodide (PI). Cells were analyzed for DNA content by FACS analysis. The percentage of cells in each phase of the cell cycle is indicated.