Rony Seger (Howard Hughes Medical Institute, University of Washington, Seattle): "MAP kinases are a family of protein kinases known to participate in a growth factor-stimulated kinase cascade. The question of how these kinases are activated attracted a considerable amount of attention. Work in our laboratory led to the identification of two forms of potent MAP kinase activator in Swiss 3T3 cells (N.G. Ahn et al., J. Biol. Chem., 226:4220-7, 1991). Although these activators promoted phosphorylation on both tyrosine and threonine residues of MAP kinase, their mechanism of action was not clear. In particular, it was important to establish whether these enzymes are protein kinases or autophosphorylation-enhancing factors.
"In this report two forms of MAP kinase 'activator' were purified to homogeneity and were shown to be capable of catalyzing the phosphorylation of an enzymatically inactive mutant of MAP kinase; phosphorylation occurred on threonine and tyrosine residues. The pure enzyme also underwent ...
