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Mouse myeloma cells in continuous culture were cloned in soft agar. The clones were assayed for their ability to synthesize heavy and light chains of gamma globulin by immunoprecipitation directly in the agar. A minor population secreting only light chains was identified. The two cell types were recloned and a low incidence of conversion of 7S to light-chain production was demonstrated. This technique can be used to isolate rare variants of cells secreting specific macromolecules.
Coffino et al. (Fri,) studied this question.