Figure 1.

The mKSR1 CA3 domain is required for the augmentation of Ras signaling. (A) Schematic representation of the WT, Myr, and CA3 mKSR1 proteins. The hatched boxes represent the five conserved areas (CA1–CA5) of the KSR family members. Pro, Cys, and S/T indicate that the corresponding CA regions are rich in proline, cysteine, or serine/threonine residues, respectively. The CRM mutation (C359S, C362S) is depicted by asterisks. For Myr mKSR1, the myristylation sequence from the src tyrosine kinase was inserted at the N terminus of WT mKSR1 (gray box). In addition, each construct contained a polyoma-derived (Pyo) epitope tag (solid box). (B) Induction of Xenopus oocyte meiotic maturation by the expression of Ras^V12 alone or by the coexpression of Ras^V12 with mKSR1 proteins. GVBD was scored when 0% of the oocytes expressing Ras^V12 alone and 40% of oocytes coexpressing Ras^V12 and WT mKSR1 had undergone GVBD. The percentage of oocytes undergoing GVBD is expressed as a solid bar, and the ratio of the number of oocytes undergoing GVBD to the total number injected is displayed above each bar. The numbers obtained represent a compilation of at least three independent experiments where equivalent amounts of the mKSR1 and Ras^V12 proteins were expressed.