de Château M, Björck L
Department of Cell and Molecular Biology, Lund University, Sweden. Maarten.de
Proc Natl Acad Sci U S A. 1996 Aug 6;93(16):8490-5. doi: 10.1073/pnas.93.16.8490.
In the evolution of eukaryotic genes, introns are believed to have played a major role in increasing the probability of favorable duplication events, chance recombinations, and exon shuffling resulting in functional hybrid proteins. As a rule, prokaryotic genes lack introns, and the examples of prokaryotic introns described do not seem to have contributed to gene evolution by exon shuffling. Still, certain protein families in modern bacteria evolve rapidly by recombination of genes, duplication of functional domains, and as shown for protein PAB of the anaerobic bacterial species Peptostreptococcus magnus, by the shuffling of an albumin-binding protein module from group C and G streptococci. Characterization of a protein PAB-related gene in a P. magnus strain with less albumin-binding activity revealed that the shuffled module was missing. Based on this fact and observations made when comparing gene sequences of this family of bacterial surface proteins interacting with albumin and/or immunoglobulin, a model is presented that can explain how this rapid intronless evolution takes place. A new kind of genetic element is introduced: the recer sequence promoting interdomain, in frame recombination and acting as a structure-less flexibility-promoting spacer in the corresponding protein. The data presented also suggest that antibiotics could represent the selective pressure behind the shuffling of protein modules in P. magnus, a member of the indigenous bacterial flora.
在真核基因的进化过程中，内含子被认为在增加有利的复制事件、偶然重组以及外显子重排导致功能性杂合蛋白的可能性方面发挥了重要作用。通常，原核基因缺乏内含子，而且所描述的原核内含子实例似乎并未通过外显子重排促进基因进化。尽管如此，现代细菌中的某些蛋白质家族通过基因重组、功能域复制而快速进化，并且如厌氧细菌大消化链球菌的蛋白质PAB所示，通过来自C组和G组链球菌的白蛋白结合蛋白模块的重排而快速进化。对大消化链球菌中一种白蛋白结合活性较低的菌株中与蛋白质PAB相关的基因进行表征发现，重排模块缺失。基于这一事实以及在比较该与白蛋白和/或免疫球蛋白相互作用的细菌表面蛋白家族的基因序列时所做的观察，提出了一个模型，该模型可以解释这种无内含子的快速进化是如何发生的。引入了一种新型遗传元件：促进结构域间读框内重组并在相应蛋白质中充当无结构的促进灵活性间隔区的recer序列。所呈现的数据还表明，抗生素可能是大消化链球菌（一种本地细菌菌群成员）中蛋白质模块重排背后的选择压力。
