Organization of class I genes in the major histocompatibility complex of the C57BL/10 mouse

We have isolated 26 different Class I genes from the C57BL/10 mouse. Overlapping cosmid clones have allowed us to organize these genes into three clusters, one mapping to the H-2K region (2 genes), one linking the H-2D and Qa2,3 regions (11 genes), and one mapping to the TL region (13 genes). The H-2K(bml) mutation seems to have been caused by gene conversion, involving the transfer of at least 13 but no more than 51 base pairs from a gene in the Qa2,3 region (the Q10 gene) to the H-2K gene. The Q10 gene is nonpolymorphic and appears to be transcribed in the liver; a protein encoded by this gene would have a truncated transmembrane domain and may be secreted. There are three homologous gene pairs in the Qa2,3 cluster suggesting that the number of genes in this region was expanded by the duplication of an ancestoral gene pair. These pairs are also homologous to the gene pair in the H-2K region; hence the H-2K region may have been generated by the translocation of a gene pair from the Qa2,3 region. Thus, this multigene family has apparently evolved by a series of gene duplication, translocation, and gene conversion events.