Signal joint of immunoglobulin V lambda 1-J lambda and novel joints of chimeric V pseudogenes on extrachromosomal circular DNA from chicken bursa.

We isolated extrachromosomal circular DNA from the bursa of 18-day chick embryos and cloned their BamHI fragments into a phage vector. We found examples of the signal joint fused by V lambda 1-J lambda rearrangement and the sequences homologous to V lambda 1 segments that showed: (1) clustered V pseudogene (psi V) germ-line segments containing new psi V26, (2) a head-to-tail duplication of psi V13-psi V12 region and (3) chimeric structures composed of 5'-V lambda 1 and 3'-psi V segments. Both intrachromosomal tandem duplications and extrachromosomal circles may be generated by unscheduled DNA synthesis and recombination. The chimeric structure of V lambda 1 joined with upstream psi V segments suggests the involvement of V gene replacement for somatic diversification of the immunoglobulin genes in addition to a mechanism of segmental gene conversion.