Multiple expression of Ig lambda-chain encoding RNA species in murine plasmacytoma cells.

The murine plasmacytoma MOPC 315, which synthesizes a complete IgA molecule containing lambda 2 light chains, is shown to synthesize a polypeptide related to the lambda 1 light chain. The abnormal lambda 1 polypeptide (m.w. approximately equal to 18,000) is encoded by a shorter polyA+ mRNA than the lambda 1 mRNAs of lambda 1-producing plasmacytomas. Polypeptides containing lambda 1-specific antigenic determinants have been found to be synthesized both in vitro by translations of RNA and in intact cells. HOPC-1, a lambda 1-producing plasmacytoma, was found to synthesize, in addition to the normal lambda 1-encoding mRNA, a lambda 2 RNA of normal length. A lambda 2-producing hybridoma does not appear to synthesize RNA encoding lambda 1 sequences. The results presented here show that more than 1 light chain gene may be transcribed within a single plasmacytoma cell. Although more than 1 light chain gene may be transcribed, the product of only 1 gene appears to be utilized for the synthesis of complete immunoglobulin molecules. This suggests novel mechanisms for the control of immunoglobulin expression.