Scheme of classical V(D)J recombination and alternative recombination mechanisms resulting in Dδ2-Dδ3 rearrangement products and circular excision products.

In classical recombination, Dδ2 and Dδ3 coding sequences are coupled to a coding joint, whereas the intervening sequence is coupled via the downstream Dδ2 RSS and the upstream Dδ3 RSS to a signal joint on the circular excision product. In the alternative mechanism that was observed in the transfected BOSC 23 cells on the basis of the sequencing of the rearrangements, a signal joint of the upstream Dδ2 RSS and the downstream Dδ3 RSS is formed, whereas the Dδ2 and Dδ3 coding sequences are deleted out on the excision circles. Primers mentioned are as follows: 1, Dδ2-5′ RO2; 2, Dδ2-lower; 3, Dδ3-upper; 4, Dδ3-3′ N.