title: Molecular evolution of vertebrate goose-type lysozyme genes.
abstract: We have found that mammalian genomes contain two lysozyme g genes. To better understand the function of the lysozyme g genes we have examined the evolution of this small gene family. The lysozyme g gene structure has been largely conserved during vertebrate evolution, except at the 5' end of the gene, which varies in number of exons. The expression pattern of the lysozyme g gene varies between species. The fish lysozyme g sequences, unlike bird and mammalian lysozyme g sequences, do not predict a signal peptide, suggesting that the encoded proteins are not secreted. The fish sequences also do not conserve cysteine residues that generate disulfide bridges in the secreted bird enzymes, supporting the hypothesis that the fish enzymes have an intracellular function. The signal peptide found in bird and mammalian lysozyme g genes may have been acquired as an exon in the ancestor of birds and mammals, or, alternatively, an exon encoding the signal peptide has been lost in fish. Both explanations account for the change in gene structure between fish and tetrapods. The mammalian lysozyme g sequences were found to have evolved at an accelerated rate, and to have not perfectly conserved the known active site catalytic triad of the bird enzymes. This observation suggests that the mammalian enzymes may have altered their biological function, as well.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, Banting and Best Diabetes Centre, Faculty of Medicine, University of Toronto, 100 College Street, M5G 1LG, Toronto, Ontario, Canada. david.irwin@utoronto.ca
authors.forename: David M
authors.initials: DM
authors.lastname: Irwin
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Gong
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001717:Birds / Q000235:genetics; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D015870:Gene Expression; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009113:Muramidase / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D021382:Protein Sorting Signals / Q000235:genetics; D051381:Rats; D017386:Sequence Homology, Amino Acid; D014714:Vertebrates / Q000235:genetics*
chemical_list: D021382:Protein Sorting Signals; D009113:Muramidase