Double recombination of a single immunoglobulin kappa-chain allele: implications for the mechanism of rearrangement.

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Abstract
DNA fragments containing Ig .kappa.-chain sequences from 2 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 2 recombination events. Each contained a variable (V.kappa.) gene segment recombined with a joining (J.kappa.) gene segment followed by the characteristic .kappa. L chain V-J reciprocal structure, a 5'' J.kappa. flanking sequence joined to a 3'' V.kappa. flanking sequence. These segments of DNA represent double recombination products (DRP) of the same .kappa.-chain allele. The DRP from PC 3609 contains a normal V-J1 recombination, while the DRP from PC 7043 contains an aberrant V-J2 resulting in a frameshift. The reciprocal structure in the PC 3609 DRP is the result of 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 .kappa.-chain gene recombination in that plasmacytoma. These products demonstrate the capacity of a single .kappa. L chain Ig allele to undergo multiple V-J recombinations. The presence of a V-J recombination and its reciprocal product in the same cells is inconsistent with a segregating mechanism, such as sister chromatid exchange, but is consistent with an inversion mechanism.