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Expressed on the membrane of immature thymocytes.

Consits of the invariant surrogate α chain, pTα , a 33 kDa glycoprotein (gp 33) disulphide-linked to a TcR β chain [1], and associated with the CD3 proteins.

Unlike the pre-BcR surrogate light chain which comprises the Vpre-B and the λ -like polypeptides non bound to the membrane, the pTα chain is a type I transmembrane protein whose cytoplasmic tail contains two potential phosphorylation sites and a Src homology 3 (SH3)-domain binding sequence [2].

A signal through the pre-TcR complex is required for cell survival and for proper transition from the DN to DP stage [3].

[1] Groettrup, M. et al. Cell 75, 283-294 (1993).
[2] Saint-Ruf, C. et al. Science 266, 1208-1212 (1994).
[3] Von Boehmer, H. et al. Curr. Opin. Immunol. 11, 135-142 (1999).