Intracellular immunoglobulin chain synthesis in non-secreting variants of a mouse myeloma: detection of inactive light-chain messenger RNA

The intracellular immunoglobulin chain content of a number of non-secreting variants of MOPC 21 mouse myeloma cells has been examined. Pulse-labelling with [¹⁴C]lysine, followed by cell lysis, reaction with antibody and analysis of the precipitates on sodium dodecyl sulphate-polyacrylamide gels, reveals three different types of variant. Only one type (NS I) contains light-chains. An abnormal heavy-chain was present in all non-secreting lines and was prominent in one cell line (NS II/1). Pulse-chase experiments indicated a rate of decay of intracellular immunoprecipitable material comparable to its rate of synthesis suggesting intracellular destruction of non-secreted chains.The presence of polyribosomes engaged in immunoglobulin chain synthesis was tested by their addition to a reticulocyte cell-free system. It was confirmed that in the parental cell line immunoglobulin chain synthesis is almost exclusively confined to membrane-derived polyribosomes. Failure of some of the variants (NS II/1 and NS III/1) to synthesize light-chain was not due to misallocation of light-chain mRNA to the free polyribosomes. Isolated 13 S mRNA from the same variants also failed to direct the synthesis of detectable light-chain in the reticulocyte cell-free system. However, fingerprint analysis of the corresponding ³²P-labelled 13 S mRNA showed the presence of several oligonucleotides characteristic of the normal light-chain mRNA, indicating the presence of an inactive form of this molecule.