Analysis of hybridoma mutants defective in synthesis of immunoglobulin M.

Hybridoma mutants defective in the expression of IgM have been analyzed by molecular and somatic cell hybridization techniques. The frequency of kappa light-chain mutants in the hybridoma PC7 was much higher than for other cell lines. In contrast to the mutations which we observed previously, the kappa mutants examined here resulted from complete or partial deletion of the kappa gene. Mutants defective in mu chain synthesis were of more diverse types including deletions, gross rearrangements, and more subtle changes. One mutant containing a cis-acting mutation resulting in reduced expression of the mu chain had an associated partial duplication of the mu gene, while others making low or undetectable levels of mu had no gross alterations in genetic structure. The usefulness of this approach to the study of gene structure and expression is discussed.