Fig. 2.

Conservation of basic TCR transmembrane residues. In the pre-TCR that is expressed in thymocytes prior to rearrangement of the TCRα locus, TCRβ forms a heterodimer with pTα. Both basic amino acids (R: arginine and K: lysine) are conserved between TCRα and pTα indicating that both αβ TCR and pre-TCR are assembled based on the same general mechanism. The three basic TCR TM residues are also conserved in the γδ TCR that is expressed by a second lineage of T cells. Only six other residues are conserved among these TM domains, and four of these represent leucine residues that are very common in TM domains due to their hydrophobic character.