lysozyme 3 to a new role, that of a digestive enzyme The acquisition of an efficient stomach lysozyme is (Dobson et al., 1984; Irwin et al., 1989 Irwin et al., , 1992; Kornegay associated with the success of the ruminants. Ad- et al., 1994). In two groups of mammals, the ruminant vanced ruminants, such as cow, sheep, and deer, have artiodactyls and the leaf-eating monkeys, and one bird, approximately 10 lysozyme genes, some of which are the hoatzin, lysozyme has been recruited for expression expressed and function in the stomach and some and function in the stomach (Dobson et al., 1984; Stewwhich are expressed and function in nonstomach tis- art et al., 1987;Kornegay et al., 1994). Lysozyme funcsues (e.g., trachea or kidney). The pig possesses a sintions in the true stomach of ruminant species to break gle conventional lysozyme c gene that is expressed in open the cell walls of bacteria that ferment plant mateboth stomach and nonstomach tissues, and in this rerial in the foregut and thereby to release their contents spect is similar to what was thought to exist in the to attack by mammalian digestive enzymes. The lysoearly artiodactyl, before the acquisition of the rumizyme gene thus provides us with an opportunity to nant lifestyle. To better understand the genetic events study the linkage between change in gene function and that occurred early in the origin and evolution of stomchange in organismal biology (Irwin et al., 1992).
ach lysozyme, we have isolated and characterized the
In artiodactyl ruminants, leaf-eating monkeys, and pig lysozyme gene. The pig lysozyme gene is similar in a leaf-eating bird, the hoatzin, lysozyme amino acid sesize to that of other mammalian species, and both quences 4 have been adapted so that it could function in stomach and nonstomach expression utilize the same the stomach, and this involved some specific amino acid promoter. All the duplications of the ruminant lysoreplacements that occurred convergently on all linzyme gene occurred after the divergence of the pig lin-