ONGOING V(X)-J(X) RECOMBINATION AFTER FORMATION OF A PRODUCTIVE V(X)-J(X) CODING JOINT

V(chi) genes of man can recombine with the J(chi) gene segments either by an inversion or by a deletion mechanism. Back-to-back fusion products of the respective recombination signal sequences (signal joints) are retained on the chromosome after the formation of a V(chi)-J(chi) coding joint by an inversion. Our knowledge of the structure of the human chi-locus and the application of the polymerase chain reaction allowed us now to establish a direct relationship between different chi recombination products in the lymphoid cell line JI. Two consecutive inversions fully explain the existence of two coding joints and two signal joints on the same chromosome of this cell line. Although the initially formed coding joint is productively rearranged and expressed, a second V(chi)-J(chi) rearrangement took place which leads to an aberrant joint. In this process a J(chi) gene segment of the signal joint that had been created in the first V(chi)-J(chi) joining was used as the recombination target. The sequence of the two rearrangements is unequivocal since a product of the first (productive) reaction is a partner in the second (aberrant) one.