Abstract
Recombination at the immunoglobulin κ or λ light chain locus generates extrachromosomal circular DNAs. We have isolated circular DNAs from adult mouse spleen cells and prepared a circular DNA clone library. We characterized four Jκ-positive and one Jλ1-positive clones. The Jκ-clones contained both coding and signal joints of Vκ-Jκ joining, and the Jλ1-clone contained a signal joint of Vλ1-Jλ1 joining. Genomic organization of the Vκ gene families used in these joints suggested the excision of circular DNA preceded by inversion. A specific dinucleotide (P) insertion in the coding joint was observed in two clones. Three coding joints were out of frame and one clone had an in-frame coding joint, although possibly combined with a pseudo-Vκ gene. These κ-positive circular DNAs are possibly excised from the chromosome by secondary recombinations which replace non-productive primary rearrangements.
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