Violations of the 12/23 rule at the mouse immunoglobulin kappa locus, including V kappa-V kappa rearrangement.

Classically, recombination between immunoglobulin gene segments uses a pair of recombination signal sequences (RSSs) with dissimilar spacers (the "12/23 rule"). Using a series of different genotyping assays, four different kinds of atypical rearrangements were identified at the murine kappa locus: (1) V kappa to V kappa, (2) J kappa to J kappa, (3) V kappa to iRS, a heptameric sequence found in the J kappa C kappa intron, and (4) a possible by-product of a rearrangement between a V kappa and the hypothetical 12-RSS side of a pre-existing signal joint. The novel V kappa-V kappa structure prompted further characterization. Sequence analysis of 14 different V kappa-V kappa rearrangements cloned from murine splenocytes and hybridomas revealed a V kappa 4 family member as one participant in 13 rearrangements, but no rearrangements contained two V kappa 4 genes. The V kappa 4 partner in the V kappa-V kappa rearrangement exhibited more trimming of nucleotides at the V kappa-V kappa junction. A signal joint derived from the inversional rearrangement of two neighboring V kappas was also recovered. These data suggest that the V kappa-V kappa structures arise via RAG-mediated, intrachromosomal recombination.