Structural similarities between surface immunoglobulins (s Ig) on B cells and antigen-specific receptors on T cells suggest that a T cell, like a B cell, should express only two immunoglobulin-like genes, one for each subunit of the disulphide-linked, heterodimeric, antigen-specific (αβ) T-cell receptor. However, cytotoxic T lymphocytes (Tc cells) and immature thymocytes also contain RNA transcripts of a third immunoglobulin-like gene, called γ (refs 1-4). A polypeptide corresponding to the γ gene has not yet been identified and the function of this gene remains an enigma. Judging from its nucleotide sequence, the rearranged γ gene is expected to encode an integral membrane polypeptide chain, and γ complementary DNAs from two cloned Tc cell lines have previously been found to have different sequences around the V-J (variable region-joining region) junction 1,2, suggesting that, in these cells, the γ-gene product is a clonally diverse surface structure that may form part of an as yet unidentified, antigen-specific receptor. To analyse further the extent of diversity of the γ-gene product, we have determined the partial sequences of 11 γ cDNA clones from three other cloned Tc cell lines, and report here that the sequences are indeed clonally diverse, but in all instances they are out-of-phase in the region of the V-J junction. This finding and the pattern of γ-gene rearrangements in these cell lines indicate that a polypeptide product of the previously reported γ gene, V2J2-C2, is not expressed in them and is, therefore, not necessary for the antigen-specific cytotoxic and proliferative responses of these mature T cells.
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