We have cloned a region of 124 kb of the human immunoglobulin lambda light chain locus on chromosome 22 encompassing seven V lambda and seven J-C lambda gene segments. No further C lambda gene segment was found in a region of 35 kb downstream of C lambda 7, which encodes the Ke+Oz- isotype. The C lambda proximal V lambda gene segment V lambda III. 1 is located 14.5 kb upstream of C lambda 1. The five sequenced V lambda genes have the same transcriptional orientation as the J-C lambda gene segments which is likely to be true for the majority of the V lambda gene segments in the human lambda locus and which suggests a deletion mechanism for DNA rearrangement. This is supported by hybridization of V lambda gene probes to germ-line and rearranged DNA from lambda light chain-producing cell lines. Sequences of 23 cDNA clones allow to establish a V lambda subgroup classification based on nucleic acid sequence data and an estimate of the J-C lambda usage.
The genes of the immunoglobulin kappa light chains are assembled during B-cell differentiation by somatic recombination of one of the V kappa (variable) gene segments and the J kappa-C kappa (joining-constant) gene region. This seems to occur by deletion of the DNa between V kappa and J kappa-C kappa if they are arranged in germ-line DNA in the same transcriptional polarity or by inversion of a fragment containing the V kappa gene if the polarities are opposite. We have cloned 75 V kappa genes and pseudogenes of the human kappa locus and linked them in large contigs. There seem to be no more than 85 such genes, less than 50 of these being potentially functional. Thirty-eight of the cloned genes have the same transcriptional polarity as J kappa-C kappa and are part of the so-called J kappa proximal cluster; 35 genes in a distal cluster (the result of a duplication event in evolution) have a polarity that was suggested to be opposite to the one of J kappa-C kappa. We now show that the V kappa genes of the proximal cluster rearrange by a deletion mechanism whereas the others join J kappa-C kappa by inversion of megabase-sized DNA fragments.
DNA digests of 16 human lymphoid cell lines were studied in blot hybridization experiments with probes from V K genes and their immediate neighborhood as well as with single or low-copy probes from intergenic regions. The patterns were compared with those of placenta DNA digests in which the genes are in the germline configuration. The differences of patterns which were detected with the first type of hybridization probes can be attributed to V K -J K rearrangements or to restriction site polymorphisms between individuals. Some of the pattern differences observed with the second type of probes can be interpreted best as arising from deletions of parts of the locus. Such deletions may be individual variations but they may also be caused by the V K -J K rearrangement process. The results obtained with one particular probe which was derived from a nonduplicated part of the locus allow some conclusions as to the mechanism of the V K -J K rearrangement: the genomic situation in some lymphoid cell lines can be explained by an inversion while in other cell lines clearly deletions have occurred. The observations are in agreement with the inversion-deletion mechanism of V* -J K rearrangement as proposed by Lewis et al. (1982Lewis et al. ( , 1984. Untersuchungen über den Immunglobulin-V^Locus von menschlichen lymphoiden ZellinienZusammenfassung: Mit Restriktionsnucleasen gespaltene DNAs aus 16 menschlichen lymphoiden Zellinien wurden in Blothybridisierungsversuchen mit Proben aus dem Immunglobulin-V K -Locus untersucht. Die Proben stammten aus V K -Genen, aus deren unmittelbarer Nachbarschaft oder aus intergenischen Regionen. Die Muster wurden mit denen von gespaltener Plazenta-DNA verglichen, in der die -Gene in der Keimbahnkonfiguration vorliegen. Unterschiede in den Hybridisierungsmustern, die mit der ersten Art von Proben entdeckt wurden, können mit V K -J K -Umlagerungen oder mit Spaltstellen-Polymorphismen erklärt werden. Einige der Unterschiede, die mit der zweiten Art von Pro-ben beobachtet wurden, können am besten auf Deletionen von Teilen des /c-Locus zurückgeführt werden. Solche Deletionen könnten individuelle Varianten oder auch durch die V K -J K -Umlagerung verursacht sein. Eine Probe, die aus einem nicht-duplizierten Teil des fc-Locus stammt, erbrachte Ergebnisse, die Rückschlüsse auf den Mechanismus der V K -J K -Umlagerung zulassen. Die genomische Situation in einigen Zellinien kann durch eine Inversion erklärt werden, während in anderen Zellinien Deletionen stattgefunden haben müssen. Die Beobachtungen passen zu dem Inversions-Deletions-Modell, wie es von Lewis et al. vorgeschlagen wurde (l982, 1984).
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