THE HUMAN IMMUNOGLOBULIN-CHI LOCUS - PSEUDOGENES, UNIQUE AND REPETITIVE SEQUENCES

The human chi locus contains 25 pseudogenes. After seven of them were described earlier the structures of the remaining 18 are reported now, thus completing the description of all human V(chi) genes and pseudogenes. Most of the pseudogenes carry several defects each. Alignments of the pseudogene sequences and comparison with the consensus sequences of the potentially functional V(chi) genes indicate that, on PCR amplification of genomic DNA aimed at certain genes of the latter class, also some of the pseudogenes would be coamplified. Unique sequences, which qualify as sequence tagged sites (STS), were defined across the locus. The occurrence of 15 repetitive elements of the LINE1 type in the locus is described. The 15 sequenced Alu elements were assigned to the known Alu subfamilies of different evolutionary age. One of the Alu elements was found only in one of the copies of the chi locus. It must, therefore, have been inserted after the duplication step which may have taken place about one million years ago. This element belongs to an Alu subfamily known to have been mobile until recently. Some aspects of the evolution of the V(chi) pseudogenes and orphons (i.e. V(chi) genes located outside the chi locus) are also discussed.