Figure 2.

Addition of Mos to a cycling extract early in interphase prevents Cdc2 activation and entry into mitosis. Cycling extracts containing sperm chromatin were supplemented with Mos (▪) or buffer (□) as soon as they were brought to room temperature (time 0) and aliquots were removed every 10 min for analysis. (A) Left, percent nuclear envelope breakdown as assessed by phase contrast microscopy. Right, histone H1 kinase activities from parallel samples. (B) Photographs of fixed nuclei stained with DAPI and observed by epifluorescence microscopy and phase-contrast microscopy. The arrows in the phase-contrast micrograph indicate the intact nuclear envelope. (C) MAP kinase immunoblots. MK, p42 MAP kinase; MK-P, phosphorylated p42 MAP kinase, which is detected by its higher apparent molecular mass.