RECIPROCAL HOMOLOGOUS RECOMBINATION IN OR NEAR ANTIBODY VDJ GENES

To determine if rearranged heavy chain variable (VDJ) genes can recomb ine with each other by crossing over of DNA strands, we constructed a transgene that contained a promoter, VDJ gene, reporter gene to detect crossover events, intron enhancer, matrix attachment region, and cons tant gene for IgM (C mu). Following immunization of transgenic mice, h ybrid molecules were isolated from B cell DNA which contained the tran sgene recombined with the endogenous IgH locus. Reciprocal products of crossovers were detected by plasmid rescue and PCR amplification, and they were sequenced. Recombination occurred somewhere within 147 bp o f homology that contained the J(H)4 gene segment and 3' flanking DNA. The recombined transgenes had a 20-fold increase in mutation in the VD J region compared to nonrecombined transgenes, which indicates that DN A sequences 3' of the C mu gene in the endogenous IgH locus are necess ary for full activity of the mutator mechanism. The recovery of recomb inants between VDJ transgenes and endogenous VDJ genes raises the poss ibility that reciprocal recombination may somatically diversify rearra nged genes between maternal and paternal alleles.