A functional gamma gene formed from known gamma-gene segments is not necessary for antigen-specific responses of murine cytotoxic T lymphocytes.

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 (alpha beta) T-cell receptor. However, cytotoxic T lymphocytes (Tc cells) and immature thymocytes also contain RNA transcripts of a third immunoglobulin-like gene, called gamma (refs 1-4). A polypeptide corresponding to the gamma gene has not yet been identified and the function of this gene remains an enigma. Judging from its nucleotide sequence, the rearranged gamma gene is expected to encode an integral membrane polypeptide chain, and gamma 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, suggesting that, in these cells, the gamma-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 gamma-gene product, we have determined the partial sequences of 11 gamma 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 gamma-gene rearrangements in these cell lines indicate that a polypeptide product of the previously reported gamma 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.