Lck is a member of the Src family of protein tyrosine kinases (PTKs).Lck is a key signaling molecule in the selection and maturation of developing T-cells.It contains N-terminal sites for myristylation and palmitylation, a PTK domain, and SH2 and SH3 domains which are involved in mediating protein-protein interactions with phosphotyrosine-containing and proline-rich motifs, respectively.