Constitutive mutant and putative regulatory serine phosphorylation site of mammalian MAP kinase kinase (MEK1).

摘要: In response to various external stimuli, MAP kinases are activated by phosphorylation on tyrosine and threonine kinase (MAPKK), a dual specificity kinase. This is in turn via Raf-1 MAPKK (MAPKKK). To determine regulatory sites of MAPKK, we isolated Chinese hamster cDNA, that epitope-tagged expressed fibroblasts. (MEK1 isoform) can reactivate recombinant p44mapk when immunoprecipitated from growth factor-stimulated cells or incubated with an active form MAPKKK. Mutations at either two residues conserved among kinases, D208N S222A, abolished activity. However, only S222A/MAPKK showed reduction MAPKKK exerted dominant negative effect the serum-stimulated endogenous MAPKK. Finally, replacing Ser222 Asp, negatively charged residue, restored activity independently upstream These results strongly suggest represents one key MAPKKK-dependent site switching off event crucial for control.