Regulatory and Structural Genes for Lysozymes of Mice

Michael F. Hammer ¹ and Allan C. Wilson ¹

¹ Department of Biochemistry, University of California, Berkeley, California 94720

The molecular and genetic basis of large differences in the concentration of P lysozyme in the small intestine has been investigated by crossing inbred strains of two species of house mouse (genus Mus). The concentration of P in domesticus is about 130-fold higher than in castaneus . An autosomal genetic element determining the concentration of P has been identified and named the P lysozyme regulator, Lzp-r . The level of P in interspecific hybrids (domesticus x castaneus) as well as in certain classes of backcross progeny is intermediate relative to parental levels, which shows that the two alleles of Lzp-r are inherited additively. There are two forms of P lysozyme in the intestine of the interspecific hybrid—one having the heat stability of domesticus P, the other being more stable and presumably the product of the castaneus P locus. These two forms occur in equal amounts, and it appears that Lzp-r acts in trans. The linkage of Lzp-r to three structural genes (Lzp-s, Lzm-s1, and Lzm-s2), one specifying P lysozyme and two specifying M lysozymes, was shown by electrophoretic analysis of backcrosses involving domesticus and castaneus and also domesticus and spretus . The role of regulatory mutations in evolution is discussed in light of these results.

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