The mouse immunoglobulin kappa locus contains about 140 variable gene segments

In continuation of our efforts to elucidate the immunoglobulin chi locus of the mouse we analyzed 46 yeast artificial chromosomes (YACs) containing V chi, J chi and C chi genes. The YACs, which were derived from DNA of C57BL/6 and C3H mice, ranged from 0.3-1.9 Mb in size. On the basis of hybridization with probes specific for the V chi gene families a group of 13 YACs was selected for detailed analysis. The V chi, genes of the YACs were then characterized by hybridization to the family-specific probes and by the sizes of the EcoRI fragments on which they were found. This way evidence was obtained for 140 different V chi gene signals on the YACs. Of these 63 had been characterized before on clones from a cosmid library of total mouse DNA (I. Zocher et al., Eur. J. Immunol. 1995. 25:3326-3331) and 22 others were found now on cosmid clones derived from the YACs. Six V chi genes of the previous study which were not found on the YACs are probably located outside of the chi locus. The YACs were arrayed in a unique order establishing a YACs panel which most likely contains the whole chi locus. The cosmid contigs and solitary cosmid clones which contain the 63 plus 22 V chi gene signals mentioned above comprise about 2.0 Mb. Assuming that the remaining 55 V chi genes are spaced at the same average distance of 24 kb, one may extrapolate to a locus size of 3.3 Mb.