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 extrachromsomal 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 Vlambda1-Jlambda rearrangement and the sequences homologous to Vlambda1 segments that showed: (1) clustered V pseudogene (psiV) germ-line segments containing new psiV26, (2) a head-to-tail duplication of psiV13-psiV12 region and (3) chimeric structures composed of 5'-Vlambda1 and 3'-psiV segments. Both intrachromosomal tandem duplications and extrachromosomal circles may be generated by unscheduled DNA synthesis and recombination. The chimeric structure of Vlambda1 joined with upstream psiV segments suggests the involvement of V gene replacement for somatic diversification of the immunoglobulin genes in addition to a mechanism of segmental gene conversion.