Immunoglobulin Cmu RNA in T lymphoma cells is not translated

It is widely believed that immunoglobulin genes might encode at least part of the receptor for antigen on the T lymphocyte. Evidence supporting this comes from the effects of anti-immunoglobulin idiotype antibodies on cellular immune networks and from the presence of idiotypes on immunologically active factors from T cells. Detailed molecular characterization of the receptors, however, has been seriously hampered by the lack of a suitable cellular source from which it might be isolated. The recent demonstration of Kemp et al. that thymocytes and certain cultured lines of mouse T lymphoma cells contain polyadenylated RNA molecules encoded by the immunoglobulin Cmu gene (Cmu RNA) prompted us to identify the corresponding protein molecules in those cells. As the haploid mouse genome contains a single Cmu gene, any polypeptide encoded by this gene should react with at least some of the antibodies present in rabbit anti-mouse IgM antiserum. In this letter we report that a number of T lymphoma lines, regardless of whether they contain Cmu RNA, synthesize no detectable mu polypeptides.