Borst P, Greaves D R
Science. 1987 Feb 6;235(4789):658-67. doi: 10.1126/science.3544215.
Programmed gene rearrangements are used in nature to to alter gene copy number (gene amplification and deletion), to create diversity by reassorting gene segments (as in the formation of mammalian immunoglobulin genes), or to control the expression of a set of genes that code for the same function (such as surface antigens). Two major mechanisms for expression control are DNA inversion and DNA transposition. In DNA inversion a DNA segment flips around and is rejoined by site-specific recombination, disconnecting or connecting a gene to sequences required for its expression. In DNA transposition a gene moves into an expression site where it displaces its predecessor by gene conversion. Gene rearrangements altering gene expression have mainly been found in some unicellular organisms. They allow a fraction of the organisms to preadapt to sudden changes in environment, that is, to alter properties such as surface antigens in the absence of an inducing stimulus. The antigenic variation that helps the causative agents of African trypanosomiasis, gonorrhea, and relapsing fever to elude host defense is controlled in this way.
在自然界中，程序性基因重排用于改变基因拷贝数（基因扩增和缺失），通过重新组合基因片段来产生多样性（如在哺乳动物免疫球蛋白基因的形成过程中），或控制一组编码相同功能的基因的表达（如表面抗原）。两种主要的表达控制机制是DNA倒位和DNA转座。在DNA倒位中，一个DNA片段翻转并通过位点特异性重组重新连接，使一个基因与表达所需的序列断开或连接。在DNA转座中，一个基因移动到一个表达位点，通过基因转换取代其先前的基因。改变基因表达的基因重排主要在一些单细胞生物中被发现。它们使一部分生物体能够预先适应环境的突然变化，即在没有诱导刺激的情况下改变诸如表面抗原等特性。非洲锥虫病、淋病和回归热的病原体所具有的有助于逃避宿主防御的抗原变异就是通过这种方式控制的。
