ICR-191 and ethyl methanesulfonate induced mutagenesis at the immunoglobulin locus in the Y5606 cultured myeloma cell line

The Y5606 mouse tumor synthesizing an IgG3, lambda immunoglobulin (Ig) was adapted to continuous growth in tissue culture. The spontaneous mutation rate at the Ig locus (approximately 3 X 10(-5)/cell/generation) in this cell line was found to be less than that in other cultured mouse myeloma lines. Treatment with either ICR-191 or ethyl methanesulfonate (EMS) increased the mutation rate approx. 100-fold. Spontaneous and ICR-191 induced mutants were synthetic variants that is they synthesized either heavy (H) or light (L) chains alone instead of the H and L chains synthesized by the parent. Following EMS treatment assembly variants which were synthesizing structurally altered H chains were isolated in addition to synthetic variants. The assembly variants appear to be a unique consequence of EMS mutagenesis.