The Z family, a group of transposed human immunoglobulin V kappa genes

A group of highly homologous transposed human V kappa I genes, which we call the Z family, was characterized. To date four members, ZI-ZIV, comprising about 230 kb, have been analyzed on cosmid clones. The largest region (ZI) has a length of 85 kb. The Z regions show extensive homology to each other according to restriction maps and hybridization data. In each Z region a solitary V kappa I gene was found. No V kappa genes of other subgroups were detected by hybridization. The nucleotide sequence of the ZI gene revealed a non-processed V kappa I pseudogene. Hybridization experiments with DNAs from rodent/human cell hybrids and other experimental data indicate that some and possibly all members of the Z family lie outside of the kappa locus which is located on chromosome 2; they have been transposed to other chromosomes. Because of their separation from the J kappa C kappa gene segment, the Z genes can be classified as pseudogenes independent of their sequences. We postulate that the Z family arose by amplification event(s). The Z regions can also be regarded as a small family of very long repetitive sequences.