Identification of two forms of the Ly-6.2 antigen showing differential expression.

A monoclonal antibody to the Ly-6.2 specificity, defined by strain and tissue distribution, was used to identify the cellular antigens of lymphocytes and tumor cell lines. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of immune precipitates demonstrated that the Ly-6.2 antigen on the surface of thymus and the T lymphoma EL-4 was a protein of 34 kd, whereas spleen cells showed two Ly-6.2 molecules of 34 kd and 56 kd. In vitro translation of EL-4 T-lymphoma poly A+ RNA followed by immunoprecipitation showed the synthesis of two Ly-6.2 precursor polypeptides. These two precursors were translated from separable mRNA molecules; the larger encoded a 54 kd polypeptide, while the second, smaller one translated a 36 kd polypeptide. Thus, the T lymphoma EL-4 contains two distinct mRNA, but only one is seen on the surface, while spleen cells contain and translate both mRNAs and both surface forms are detected. What determines the utilization of the two mRNAs and the surface expression of the two different proteins in the different tissues is not known. Whether the two mRNAs are the transcripts of one gene or arise by transcription of two separate but closely linked genes remains to be determined.