MOLECULAR CLONING OF PTAC12 AN ALTERNATIVE SPLICING PRODUCT OF THE CD3GAMMA CHAIN AS A COMPONENT OF THE PRE-T CELL ANTIGEN-RECEPTOR COMPLEX

Abstract We have reported that a 12-kDa molecule (pTAC12 as a pre-T cell receptor (TCR)-associated chain) was associated as a dimer with the pre-TCR complex as well as the clonotype-independent CD3 complex on the cell surface of immature thymocytes. We now report by protein sequencing and molecular cloning that pTAC12 is an alternatively spliced product of the CD3γ chain lacking exon 4 containing the transmembrane region. The transcript of pTAC12 is expressed in most T cell lineages and parallels the expression of CD3γ. However, the pTAC12 protein is expressed on the cell surface of immature thymocytes but not mature T cells, despite the fact that mature T cells express a low level of pTAC12 in association with the TCR complex within the cells. These results indicate that pTAC12 may play a special role for the transport/expression and assembly of the pre-TCR·CD3 complex as well as the clonotype-independent CD3 complex in immature thymocytes.