Dual expression of lambda genes in the MOPC-315 plasmacytoma.

The expression of two kappa light chain immunoglobulins in the MPC-11 mouse myeloma is well established, the two protein products being apparently from RNA transcripts derived from separate, rearranged kappa alleles in the MPC-11 genome. Recently, the characterization of kappa-related RNAs and protein products in several lambda-producing myelomas has indicated that multiple expression of light chain RNAs is a common event in myelomas and other cells of the B-lymphocyte lineage. These studies suggest that, although many light chain alleles may function to make RNA and protein in a given B-lymphocytic cell, only one complete, functional light chain is generally translated from the RNAs present in a single cell. The myeloma, MOPC-315, synthesizes and secretes an antibody which has an alpha heavy chain and a lambda II light chain. The DNA of MOPC-315 either has no kappa genes or has only a fragment of one, but it certainly has no kappa genes in the embryonic configuration. Rearrangement of its lambda genes has been observed but the exact nature of the rearrangement is not known. Because initial observations suggested that an immunoglobulin-related protein other than alpha and lambda II was present in MOPC-315 cells, we undertook to derive molecular cDNA clones from the MRNA in MOPC-315 tumour cells. Analysis of the clones has now identified two lambda chain mRNA species: a normal lambda II chain mRNA and another which directs the synthesis of a deleted form of a lambda I protein. The nucleotide sequence of the deleted lambda I mRNA shows that it resulted from a joining of the sequence encoding amino acid 31 of the variable region directly to the constant region coding sequence.