Mutant immunoglobulin genes have repetitive DNA elements inserted into their intervening sequences.

Abstract
The .kappa. L chain genes from 2 mutant hybridoma cell lines defective in .kappa. L chain synthesis were isolated and compared to the wild-type .kappa. L chain gene. The mutant .kappa. L chain genes were found to contain repetitive DNA elements in their intervening sequences that were not present in the intervening sequences of the wild-type .kappa. L chain gene. These elements were found to be related to the genes of intracisternal A particles. The decreased production of .kappa. L chain in the mutant cell lines is due to the presence of the intracisternal A particle-related genes.