Figure 3.

Addition of constitutively active Mek to cycling extracts in early interphase activates MAP kinase and prevents Cdc2 activation. Cycling extracts containing sperm chromatin were supplemented with Mek (▪) or buffer (□) at time 0, and aliquots were removed every 10 min for analysis. (A) Left, percent nuclear envelope breakdown, monitored by phase-contrast microscopy. Right, H1 kinase activity. (B) MAP kinase immunoblots. Phosphorylated (shifted) MAP kinase is visible in the Mek-treated extracts but not in the buffer-treated extracts. The active MK lane shows fully active MAP kinase from a CSF-arrested extract. MK, p42 MAP kinase.