A, W303 cells, in the presence of α factor, and cdc4-1 cells were grown in 2% raffinose medium at 37 °C for 2 h. c-Myc expression was induced for 1 h at 37 °C by the addition of galactose. After termination of expression by the addition of glucose, cells were harvested at the indicated time points and lysed in SDS sample buffer. Western blotting and quantitation were performed as described in Fig. 1B. B, schematics of the Homo sapiens (h.s.) F-box protein, Fbw7, and the S. cerevisiae (s.c.) F-box protein, Cdc4. Key structural domains are indicated as well as target proteins of the F-boxes that are important in regulating the cell cycle (see “Results”).