MOLECULAR-CLONING OF PTAC12 AN ALTERNATIVE SPLICING PRODUCT OF THE CD3-GAMMA CHAIN AS A COMPONENT OF THE PRE-T CELL ANTIGEN-RECEPTOR COMPLEX

We have reported that a 12-kDa molecule (pTAC12 as a pre-T cell recept or (TCR)-associated chain) was associated as a dimer with the pre-TCR complex as well as the clonotype-independent CD3 complex on the cell s urface of immature thymocytes. We now report by protein sequencing and molecular cloning that pTAC12 is an alternatively spliced product of the CD3 gamma chain lacking exon 4 containing the transmembrane region . The transcript of pTAC12 is expressed in most T cell lineages and pa rallels the expression of CD3 gamma. However, the pTAC12 protein is ex pressed on the cell surface of immature thymocytes but not mature T ce lls, despite the fact that mature T cells express a low level of pTAC1 2 in association with the TCR complex within the cells. These results indicate that pTAC12 may play a special role for the transport/express ion and assembly of the pre-TCR-CD3 complex as well as the clonotype-i ndependent CD3 complex in immature thymocytes.