Lawrence J G, Roth J R
Department of Biology, University of Utah, Salt Lake City 84112, USA.
Genetics. 1996 Aug;143(4):1843-60. doi: 10.1093/genetics/143.4.1843.
A model is presented whereby the formation of gene clusters in bacteria is mediated by transfer of DNA within and among taxa. Bacterial operons are typically composed of genes whose products contribute to a single function. If this function is subject to weak selection or to long periods with no selection, the contributing genes may accumulate mutations and be lost by genetic drift. From a cell's perspective, once several genes are lost, the function can be restored only if all missing genes were acquired simultaneously by lateral transfer. The probability of transfer of multiple genes increases when genes are physically proximate. From a gene's perspective horizontal transfer provides a way to escape evolutionary loss by allowing colonization of organisms lacking the encoded functions. Since organism bearing clustered genes are more likely to act as successful donors, clustered genes would spread among bacterial genomes. The physical proximity of genes may be considered a selfish property of the operon since it affects the probability of successful horizontal transfer but may provide no physiological benefit to the host. This process predicts a mosaic structure of modern genomes in which ancestral chromosomal material is interspersed with novel, horizontally transferred operons providing peripheral metabolic functions.
本文提出了一种模型，即细菌中基因簇的形成是由DNA在分类群内部和之间的转移介导的。细菌操纵子通常由其产物有助于单一功能的基因组成。如果这种功能受到弱选择或长时间无选择，相关基因可能会积累突变并因遗传漂变而丢失。从细胞的角度来看，一旦几个基因丢失，只有当所有缺失的基因通过横向转移同时获得时，功能才能恢复。当基因在物理上相邻时，多个基因转移的概率会增加。从基因的角度来看，水平转移提供了一种通过允许在缺乏编码功能的生物体中定殖来逃避进化损失的方式。由于携带成簇基因的生物体更有可能成为成功的供体，成簇基因将在细菌基因组中传播。基因的物理相邻性可能被认为是操纵子的一种自私特性，因为它影响成功水平转移的概率，但可能不会为宿主提供生理益处。这一过程预测了现代基因组的镶嵌结构，其中祖先染色体物质与提供外围代谢功能的新型水平转移操纵子相互穿插。
