Background |
The Src family of protein tyrosine kinases, which includes Src, Lyn, Fyn, Yes, Lck, Blk, and Hck, are important in the regulation of growth and differentiation of eukaryotic cells (1). Src activity is regulated by tyrosine phosphorylation at two sites, but with opposing effects. While phosphorylation at Tyr416 in the activation loop of the kinase domain upregulates enzyme activity, phosphorylation at Tyr527 in the carboxy-terminal tail by Csk renders the enzyme less active (2). Lck is essential for T-lymphocyte activation and differentiation (3,4). Phosphorylation of Tyr505 in the carboxy-terminal tail of Lck downregulates its catalytic activity, while phosphorylation of Tyr394 leads to an increase in Lck activity (5).
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