Irwin D M, White R T, Wilson A C
Division of Biochemistry and Molecular Biology, University of California, Berkeley 94720.
J Mol Evol. 1993 Oct;37(4):355-66. doi: 10.1007/BF00178866.
Cow stomach lysozyme genes have evolved in a mosaic pattern. The majority of the intronic and flanking sequences show an amount of sequence difference consistent with divergent evolution since duplication of the genes 40-50 million years ago. In contrast, exons 1, 2, and 4 and immediately adjacent intronic sequences differ little between genes and show evidence of recent concerted evolution. Exon 3 appears to be evolving divergently. The three characterized genes vary from 5.6 to 7.9 kilobases in length. Different distributions of repetitive DNA are found in each gene, which accounts for the majority of length differences between genes. The different distributions of repetitive DNA in each gene suggest the repetitive elements were inserted into each gene after the duplications that give rise to these three genes and provide additional support for divergent evolution for the majority of each gene. The observation that intronic and flanking sequences are evolving divergently suggests that the concerted evolution events involved in homogenizing 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.
牛胃溶菌酶基因以镶嵌模式进化。大多数内含子和侧翼序列显示出一定程度的序列差异，这与4000万至5000万年前基因复制后的趋异进化一致。相比之下，基因之间的外显子1、2和4以及紧邻的内含子序列差异很小，并显示出近期协同进化的证据。外显子3似乎在趋异进化。三个已鉴定的基因长度在5.6至7.9千碱基之间变化。每个基因中重复DNA的分布不同，这是基因之间长度差异的主要原因。每个基因中重复DNA的不同分布表明，重复元件是在产生这三个基因的复制之后插入到每个基因中的，并为每个基因的大部分趋异进化提供了额外支持。内含子和侧翼序列趋异进化的观察结果表明，使溶菌酶基因编码区同质化的协同进化事件一次只涉及一个外显子。这种协同进化模型将允许基因之间外显子大小的信息片段进行重排，这种现象可能有助于胃溶菌酶的早期适应性进化。
