Abstract
After mutagenesis of cultured mouse myeloma cells with ICR 191 or Melphalan, variant clones were isolated that synthesized immunoglobulin heavy chains shorter than those produced by the parent. These variants fell into two phenotypes, based on the size, serology, and pattern of assembly of the heavy chain. Variant chains of both types no longer reacted with antisera directed either against the Fc (C-terminal half of the heavy chains) or subclass-specific IgG(2b) determinants. Comparative ion exchange chromatography of tryptic-chymotryptic peptides confirmed that the variant heavy chains differed structurally from those of the parent and from each other. A conversion from one phenotype to the other has been observed.