Figure 5.

The MAPK pathway is not critical for Greatwall-induced activation of Cdc25. The involvement of the MAPK pathway in Greatwall-induced mitotic entry was tested in interphase extracts released from CSF arrest by the addition of CaCl₂ at t = 0. Extracts were then incubated at 23°C for 30 min before U0126 was supplemented to a final concentration of 400 μM as shown. After 10 min of incubation, excess active Greatwall was added as indicated. Immunoblot analysis reveals that U0126 shuts down signaling through the MAPK pathway, but does not interfere with Greatwall's ability to induce Cdc25 phosphorylation and precocious mitotic entry.