FIG. 3.

MPF requires MAPK activity to induce Mos protein accumulation and Mos UTRX polyadenylation. Immature oocytes were preincubated with 100 μM MEK inhibitor (MI), as indicated, prior to injection with RNA encoding cyclin B1. When cyclin and progesterone-stimulated control oocytes had reached GVBD₅₀, pools of oocytes were harvested and both protein lysates and total RNA were prepared. (A) Protein lysates were analyzed for Mos protein expression (top panel) and kinase activation (lower panels) as described in the legend to Fig. 1. (B) RNA samples were incubated with RNase H, with or without oligo(dT) as indicated, and Mos UTRX polyadenylation was analyzed as described in the legend to Fig. 2B.