Myf5 can occupy the promoter of Cdc6 in MyoD^−/− primary myoblasts and in MyoD-depleted quiescent myoblasts after serum stimulation. (A and B) Cross-linked chromatin prepared from quiescent C2C12 myoblasts expressing shMyoD-66 after stimulation by serum for periods of 6 or 12 h was immunoprecipitated in parallel with anti-Myf5 and normal rabbit IgG (NR IgG). Semiquantitative PCR was then performed with the use of primers surrounding the E-box site E1 within the Cdc6 promoter. Black lines indicate that intervening lanes have been spliced out. (C) Crossed-linked chromatin from cultured MyoD^−/− primary myoblasts was immunoprecipitated in parallel with anti-Myf5 or anti-MyoD antibody (Ab) and then analyzed by semiquantitative PCR using primers surrounding the E-box sites (E1 and E2) within the Cdc6 promoter. A control reaction with the use of normal rabbit IgG is shown along with input DNA, which was amplified by the same set of primers.