C-Src Tyrosine Kinase (CSK)

C-src tyrosine kinase includes an SH2 domain, an SH3 domain, and a tyrosine kinase domain. This protein specifically phosphorylates Tyr-504 residue on human leukocyte-specific protein tyrosine kinase, which acts as a negative regulatory site. It may also act on the LYN and FYN kinases.

CSK downregulates tyrosine kinase activity of the SRC oncoprotein  through tyrosine phosphorylation of the SRC carboxy terminus. Since cell transformation by SRC oncoproteins is caused by various mechanisms that interfere with this phosphorylation, the CSK gene might function as an antioncogene .