Structure of class II genes in wild mouseMus saxicola: functional and evolutionary implications

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Abstract
Class II β genes have been characterized from Mus saxicola, a wild mouse which diverged five millions years ago from the house mouse. The nucleotide sequences of the exons 2 and 3 of Eβ1, Aβ2 and Eβ2 genes have been determined in order to define the molecular mechanisms of interspecies variability. The Eβ1 and Aβ1 (J. X. She, personal communication) genes from Mus saxicola display extensive sequence variability in exon 2 when compared tothose of the house mouse, in association with the variability of residues probably involved in antigen binding. On the other hand, most putative T cell contact residues from the I-Eβ chain, and to a lesser extent from the I-Aβ chain, were found conserved in mice. T cell contact residues from Mus saxicola I-Aβ and I-Eβ chains are identical to those of the b and q, and of the k haplotypes of the house mouse, respectively. Comparisons performed withAβ2 and Eβ2 genes revealed that both are highly conserved and, in contrast to Aβ1 and Eβ1 genes, that a strong selective pressure for conservation occurs in the Aβ2 second exon. The different aspects of Aβ2 and Eβ2 genes evolution may correlate with the original function of their products. Comparisons of the intervening sequences revealed that the repeated motifs of the hotspot region present in the Eβ1b gene are also conserved in Mus saxicola. Recombinations may have occurred, in some cases in association with χ-like sequences.