Double recombination of a single immunoglobulin κ-chain allele: Implications for the mechanism of rearrangement

DNA fragments containing immunoglobulin κ-chain sequences from two different plasmacytomas (PC 3609 and PC 7043) were found by blot-hybridization studies to be dissociated from germ-line sequences on both the 3' and 5' ends. These fragments were cloned, sequenced, and found to contain the structural features of a product of two recombination events. Each contained a variable (V(κ)) gene segment recombined with a joining (J(κ)) gene segment followed by the characteristic κ light chain V-J reciprocal structure, a 5' J(κ) flanking sequence joined to a 3' V(κ) flanking sequence. These segments of DNA represent double recombination products (DRPs) of the same κ-chain allele. The DRP from PC 3609 contains a normal V-J1 recombination, while the DRP from PC 7043 contains an aberrant V-J2 recombination, resulting in a frameshift. The reciprocal structure in the PC 3609 DRP is the result of a V-J2 recombination; the reciprocal structure in the DRP of PC 7043 is the result of a V-J3 recombination and appears to have been derived directly from the productive κ-chain gene recombination in that plasmacytoma. These products demonstrate the capacity of a single κ light chain immunoglobulin allele to undergo multiple V-J recombinations. Furthermore, the presence of a V-J recombination and its reciprocal product in the same cell is inconsistent with a segregating mechanism, such as sister chromatid exchange, but is consistent with an inversion mechanism.