CHARACTERIZATION OF THE COW STOMACH LYSOZYME GENES - REPETITIVE DNA AND CONCERTED EVOLUTION

Cow stomach lysozyme genes have evolved in a mosaic pattern. The major ity of the intronic and flanking sequences show an amount of sequence difference consistent with divergent evolution since duplication of th e genes 40-50 million years ago. In contrast, exons 1, 2, and 4 and im mediately adjacent intronic sequences differ little between genes and show evidence of recent concerted evolution. Exon 3 appears to be evol ving divergently. The three characterized genes vary from 5.6 to 7.9 k ilobases in length. Different distributions of repetitive DNA are foun d in each gene, which accounts for the majority of length differences between genes. The different distributions of repetitive DNA in each g ene suggest the repetitive elements were inserted into each gene after the duplications that give rise to these three genes and provide addi tional support for divergent evolution for the majority of each gene. The observation that intronic and flanking sequences are evolving dive rgently suggests that the concerted evolution events involved in homog enizing the coding regions of lysozyme genes involve only one exon at a time. This model of concerted evolution would allow the shuffling of exon-sized pieces of information between genes, a phenomenon that may have aided in the early adaptive evolution of stomach lysozyme.