A potential donor gene for the bm1 gene conversion event in the C57BL mouse

Abstract

The mammalian major histocompatibility complex (MHC; H–2 complex in mouse) is a large multigene complex which encodes cell-surface antigens involved in the cellular immune response to foreign antigens¹. Class I polypeptides expressed at the H–2K and H–2D (Fig. 1) loci of numerous mouse strains exhibit an unusually high degree of genetic polymorphism, which is assumed to be related to their function as primary recognition elements in the immune response. We suggested that this H–2 polymorphism may arise by gene conversion-like events between non-allelic class I genes. This is supported by our recent comparison of the DNA sequences of the normal H–2K^b gene sequence, from the C57BL/10 mouse, and a mutant^2,3 form of this gene called H–2K^bm1 (ref. 4): the mutant allele differs from the H–2K^b gene in seven bases out of a region of 13 bases in exon 3 of the class I gene (which encodes α₂ (C1) the second highly polymorphic protein domain), suggesting that this region of new sequence had been introduced into the H–2K^b sequence following unequal pairing of two class I genes in the genome of the C57BL mouse. Schulze et al. have obtained similar results⁵. Here we report work identifying a potential donor gene in our library of 26 class I genes cloned from the C57BL/10 mouse.