Immune precipitation of immunoglobulin producing polysomes from mouse myeloma cells

MPC 11 myeloma cells synthesizing IgG were labeled in vitro with [³H]uridine and the cell lysates, or purified polysomes, treated with rabbit antiserum against the purified MPC 11 protein. The specificity of the immune precipitation was tested by rabbit anti egg albumin and by precipitation of polysomes from 'non producer' myeloma and HeLa cells. The specific precipitation was 10 to 15% of the total cytoplasmic RNA for the IgG producing clone of MPC 11 and about 2% for the non producer clone or HeLa cells. Up to 20% of the total polysomal and ribosomal RNA were precipitated from the IgG producing clone. This value correlated with the IgG synthesis of these cells which is also about 20% of the total protein produced. The results suggest that myeloma cells produce a relatively large quantity of IgG due to the presence of a large amount of specific mRNA molecules.