ECTOPIC RECOMBINATION WITHIN HOMOLOGOUS IMMUNOGLOBULIN-MU GENE CONSTANT REGIONS IN A MOUSE HYBRIDOMA CELL-LINE

We have transferred a pSV2neo vector containing the wild-type constant region of the immunoglobulin mu gene (Cmu) into the mutant hybridoma igm482, which bears a 2-bp deletion in the third constant-region exon of its haploid chromosomal mu gene (Cmu3). Independent igm482 transformants contain the wild-type immunoglobulin Cmu region stably integrated in ectopic chromosomal positions. We report here that the wild-type immunoglobulin Cmu region can function as the donor sequence in a gene conversion event which corrects the 2-bp deletion in the mutant igm482 chromosomal Cmu3 exon. The homologous recombination event restores normal immunoglobulin M production in the mutant cell.