Rony Seger (University of Washington, Seattle): “Protein kinases were traditionally classified into two main subgroups: those that phosphorylate serine or threonine residues on their protein substrates and those that phosphorylate tyrosine residues. However, several protein kinases recently have been shown to phosphorylate both types of residues. Our paper was one of the firstto describe these 'dual-specificity kinases,' showing that the mitogen-activated protein (MAP) kinases, ERK1 and ERK2, undergo autophosphorylation on both tyrosine and threonine residues.
“Although the number of dual-specificity kinases is constantly growing, the physiological relevance of many of them is not well understood (R.A. Lindberg, et al., Trends In Biochemical Sciences, 17:114-9, 1992). Our finding—that the autophosphorylation of MAP kinases occurs on threonine and tyrosine residues as the in vivo regulatory phosphorylation (N.G. Anderson, et al., Nature, 343:651-3, 1990) and is accompanied by some autoactivation—led us to propose that this autophosphorylation might be involved in the MAP kinase...
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