ACTIVITY AND AUTOPHOSPHORYLATION OF LAMMER PROTEIN-KINASES

Clk/STY, the murine homologue of the recently described LAMMER family of protein kinases, autophosphorylates on serine/threonine and tyrosin e residues in vitro and in, vivo, LAMMER kinases are found throughout eukaryotes and possess virtually complete amino acid identity in many domains critical for kinase function, leading to the question of wheth er other family members also possess dual specificity. We report here that the Drosophila family member DOA, human SK-G1, and the Saccharomy ces cerevisiae KNS1, all possess protein kinase activity and autophosp horylate with dual specificity in vitro, suggesting that the entire fa mily possesses this activity. Although the LAMMER kinases are closely related to the mitogen-activated protein kinase family, they possess d ifferent substrate specificity in vitro, based on phosphorylation of p eptide and protein substrates and sequencing of a phosphorylation site in a common substrate.