The phosphorylation of proteins by protein kinases and protein phosphatases is a key event in most nuclear and cytoplasmic processes. The ability to activate and deactivate proteins via phosphorylation or dephosphorylation is important for cell division, cell differentiation, DNA repair and transcription. LMTK3 (lemur tyrosine kinase 3), also known as LMR3 or TYKLM3, is a 1,460 amino acid protein that contains one protein kinase domain. One of several members of the protein kinase superfamily, LMTK3 is expressed at low levels in brain and testis where it catalyzes the ATP-dependent phosphorylation of target proteins, thereby modifying their function.