Novel strand exchanges in V(D)J recombination.

We describe novel products of V(D)J recombination in which signal sequences become joined to coding elements, in contrast to the standard reaction whose products are junctions of two signal sequences or two coding elements. In this variant reaction, the recombination machinery evidently recognizes signal sequences and introduces strand breaks at the normal positions, but then connects the elements in unusual combinations. The lack of fixed directionality indicates that recombination sites are not uniquely aligned when strand exchange occurs. The discovery of these variant junctions suggests a model for the evolution of the antigen receptor loci.