Fig. 4. Ectopic expression of MKP3 blocks RAS/MAPK signaling. (A) mkp3 expression constructs. Sequence represents the phosphatase active site. (B) Xenopus animal explant assay. Explants injected with activated forms of RAS exhibit induction of Xbra, while co-injection of mkp3 suppresses RAS activity. The inactive mutant construct mkp3::C292S had no effect on the activated form of RAS. (C-J) Ectopic expression of mkp3 or mkp3::C292S can suppress or enhance, respectively, the expression of sef and spry4 at gastrula stage.