Could play a significant role in the signal transduction of hematopoietic cells. May regulate tyrosine kinase activity of SRC-family members in brain by specifically phosphorylating their C-terminal regulatory tyrosine residue which acts as a negative regulatory site. It may play an inhibitory role in the control of T-cell proliferation. ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Interacts with KIT. In platelets, 90% of MATK localizes to the membrane fraction, and translocates to the cytoskeleton upon thrombin stimulation. Expressed in various myeloid cell lines, detected in brain and lung. Belongs to the protein kinase superfamily. Tyr protein kinase family. CSK subfamily.