Activation of T cells by a tyrosine kinase activation domain in the cytoplasmic tail of CD3 epsilon.

The multichain T cell antigen receptor functions by interacting with and activating one or more nonreceptor tyrosine kinases. The cytoplasmic tail of the zeta chain can activate T cells independently of the rest of the receptor complex. The function of the remaining invariant CD3 chains remains unknown. A 22-amino acid region of the cytoplasmic tail of CD3 epsilon was also able to independently activate T cells. Stimulation of T cells by means of the cytoplasmic tails of either zeta or CD3 epsilon resulted in quantitatively distinct patterns of tyrosine phosphorylation, suggesting activation of different biochemical pathways.