Ongoing Vx−Jx recombination after formation of a productiveVx−Jx coding joint

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Abstract
Vx genes of man can recombine with the Jx gene segments eitherbyan 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 Vx−Jx coding joint by an inversion. Our knowledge of the structure of the human x locus and the application of the polymerase chain reaction allowed us now to establish a direct relationshipbetween different x 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 Vx−Jx rearrangement took place which leads to an aberrant joint. In this process a Jx gene segment of the signal joint that had been created in the first Vx−Jx 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.