An immunoglobulin heavy chain gene deletion at direct repeats: nucleotide sequence and effect on mRNA accumulation

The DNA from the mouse myeloma cell, I17, which produces aberrant gamma 2b heavy chain mRNAs, was cloned and sequenced. The I17 mutant, and its parent line 10.1, share a small deletion at the splice junction of the CH1 domain which results in the absence of CH1 sequences from the mRNA. In addition, the genomic DNA of I17 has a deletion of 253 nucleotides which fuses the CH2 and CH3 exons, causes a frameshift of the next 43 amino acids and results in a truncated protein. The deleted nucleotides are flanked by two direct repeats of the CAGCA pentamer in the normal gene. One copy of the repeat and the interposed DNA is removed in the mutant. The DNA deletion is colinear with the mRNA. Both I17 and 10.1 cells have decreased accumulation of the secretory-specific gamma 2b mRNA. The amounts of membrane-specific gamma 2b mRNA are also affected in the mutants.