catalytic activity:ATP + a [protein]-L-tyrosine = ADP + a [protein]-L-tyrosine phosphate.,function:Specifically phosphorylates 'Tyr-504' on LCK, which acts as a negative regulatory site. Can also act on the LYN and FYN kinases.,PTM:Autophosphorylation of Tyr-304 occurs only at abnormally high CSK concentrations in vitro.,similarity:Belongs to the protein kinase superfamily. Tyr protein kinase family.,similarity:Belongs to the protein kinase superfamily. Tyr protein kinase family. CSK subfamily.,similarity:Contains 1 protein kinase domain.,similarity:Contains 1 SH2 domain.,similarity:Contains 1 SH3 domain.,subcellular location:Mainly cytoplasmic, also present in lipid rafts.,subunit:Interacts with PTPN8 (By similarity). Interacts with phosphorylated SIT1, PAG1, LIME1 and TGFB1I1.,tissue specificity:Expressed in lung and macrophages.,