Figure 1.

Reg/Raf inhibits the biological and enzymatic activity of Cat/Raf. (A) Schematic depiction of the Reg/Raf and Cat/Raf proteins. (B) Effect of Reg/Raf on Xenopus oocyte meiotic maturation. Oocytes were injected with buffer (−) or RNA encoding the Reg/Raf protein (+). Four to eight hours later, the oocytes were injected with RNA encoding Cat/Raf-1, Ha-Ras^V12, Tpr-Met, or v-Mos or were treated with progesterone (Prog). GVBD was then scored. Numbers shown represent a compilation of at least five (Cat/Raf) or two (Ha-Ras^V12, Tpr-Met, v-Mos, Prog) independent experiments where equivalent amounts of Reg/Raf proteins were expressed. (C) Reg/Raf inhibits the enzymatic activity of Cat/Raf and the activation of MEK1 and MAPK. Cat/Raf (Top), MEK1 (Middle), and MAPK (Bottom) proteins were immunoprecipitated from Xenopus oocytes expressing Cat/Raf alone (−) or coexpressing Cat/Raf and Reg/Raf (+), and in vitro protein kinase assays were performed. The positions of MEK1, glutathione S-transferase (GST)-MAPK, or myelin basic protein (MBP), used as exogenous substrates in these assays, are indicated.