The human immunoglobulin kappa locus on yeast artificial chromosomes (YACs)

The human immunoglobulin kappa locus is a duplicated structure. Contigs of 600 kb with 40 Vkappa genes and 440 kb with 36 Vkappa genes had been established for the Ckappa proximal (p) and distal (d) copies, respectively. In addition the human genome contains more than 24 dispersed Vkappa genes, called orphons. In the present study, 22 kappa-locus derived YACs were analyzed in detail, while 30 orphon-derived YACs were characterized only with respect to some parameters. The kappa-locus derived YACs allowed three gaps to be closed which previously could not be bridged by cosmid and phage lambda cloning. At the 5' side, the p contig was extended in the YACs by 50 kb and the d contig by 16 kb. At the 3'side, the d contig was extended by 11.5 kb. Beyond the 3' end of the d contig a new Vkappa gene was found, which is located, according to pulsed field gel electrophoresis (PFGE) experiments, at a distance of at least 140 kb from the last Vkappa gene of the contig. This Vkappa gene, which was termed Z0, occurred on three YACs, albeit at distances smaller than 140 kb; this was probably due to deletions in the YACs caused by abundant repetitive sequences at the borders of the locus. According to its sequence and to the restriction map of its surroundings, Z0 is an orphon gene of the so-called Z family, of which several members are known to be dispersed throughout the genome. The possibility that Z0 has been the parent of the other Z orphons is discussed.