Recombining sequence recombination in normal kappa-chain-expressing B cells.

Recombining sequence (RS) recombination is a DNA rearrangement that deletes one or two C kappa alleles in a large proportion of lambda-expressing B cells. Since its discovery, this recombination has been suggested to play a role in activating lambda gene rearrangements. A model involving a positive signal generated by RS recombination seems to be excluded, but another model that is still under consideration proposes that RS recombination removes DNA sequences within the kappa locus that would interfere with lambda gene assembly. Using PCR assays, we have found that kappa-expressing cells account for the majority of RS rearrangements in mouse spleen. RS rearrangements were also detected by Southern blot in kappa-secreting hybridomas. Quantification of rearrangements indicates that approximately 12% of kappa cells bear an RS recombination. From this finding, we infer that once a cell has performed an RS recombination on one kappa allele, it has a 3 times higher probability of rearranging functionally its other kappa allele rather than one of the lambda genes. These data call into question the role of RS recombination in the switch from kappa to lambda and suggest another function for this nonproductive rearrangement.