This gene encodes an enzyme belonging to the protein
tyrosine kinase family, and it plays a role in T-cell development
and lymphocyte activation. This enzyme, which is phosphorylated on
tyrosine residues upon T-cell antigen receptor (TCR) stimulation,
functions in the initial step of TCR-mediated signal transduction
in combination with the Src family kinases, Lck and Fyn. This
enzyme is also essential for thymocyte development. Mutations in
this gene cause selective T-cell defect, a severe combined
immunodeficiency disease characterized by a selective absence of
CD8-positive T-cells. Two transcript variants that encode different
isoforms have been found for this gene.
