Human light chain genes are used in a κ before λ order. Accompanying this hierarchy is the rearrangement of a κ-deleting element (Kde) which eliminates the kappa locus before λ gene rearrangement. In approximately 60% of rearrangements the Kde recombines at a conserved heptamer within the Jκ-Cκ intron. We demonstrated that aberrant V/J rearrangements possessing apparent N nucleotides existed 5\u27 to the Jκ-Kde rearrangements. This suggests that the Kde may selectively eliminate nonfunctional V/J alleles. A κ-producing cell that displayed the unusual finding of λ gene rearrangement demonstrated a rearranged Kde. This rearrangement was a Vκ/Kde recombination and the heptamer-11 bp spacer-nonamer flanking the Vκ is the target site of the Kde 40% of the time. The mouse possesses a counterpart to the Kde (recombining sequence [RS]) and the highly conserved regions surround the heptamer-spacer-nonamer signals. No complete protein product was predicted from the germline Kde near its break-point and no consistent fusion product was predicted from either the V/Kde or V/J-Kde rearrangements. A distal portion of the Kde is duplicated and is present at 2q11 as well as 2p11. The evolutionary conservation of the kappa-elimination event, the duplication and maintenance of the Kde indicates that it has a function. A portion of the Kde may still prove to encode a trans-acting factor that directly affects λ rearrangement. A certain role for the Kde is its site-specific rearrangement, which destroys ineffective κ genes and sets the stage for λ gene utilization
