Zinser Erik R, Schneider Dominique, Blot Michel, Kolter Roberto
Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
Genetics. 2003 Aug;164(4):1271-7. doi: 10.1093/genetics/164.4.1271.
The loss of preexisting genes or gene activities during evolution is a major mechanism of ecological specialization. Evolutionary processes that can account for gene loss or inactivation have so far been restricted to one of two mechanisms: direct selection for the loss of gene activities that are disadvantageous under the conditions of selection (i.e., antagonistic pleiotropy) and selection-independent genetic drift of neutral (or nearly neutral) mutations (i.e., mutation accumulation). In this study we demonstrate with an evolved strain of Escherichia coli that a third, distinct mechanism exists by which gene activities can be lost. This selection-dependent mechanism involves the expropriation of one gene's upstream regulatory element by a second gene via a homologous recombination event. Resulting from this genetic exchange is the activation of the second gene and a concomitant inactivation of the first gene. This gene-for-gene expression tradeoff provides a net fitness gain, even if the forfeited activity of the first gene can play a positive role in fitness under the conditions of selection.
在进化过程中，已有基因或基因活性的丧失是生态特化的主要机制。迄今为止，能够解释基因丧失或失活的进化过程仅限于两种机制之一：直接选择在选择条件下不利的基因活性丧失（即拮抗多效性），以及中性（或近中性）突变的与选择无关的遗传漂变（即突变积累）。在本研究中，我们用一株进化的大肠杆菌证明，存在第三种不同的机制，通过该机制基因活性可能会丧失。这种依赖于选择的机制涉及第二个基因通过同源重组事件征用第一个基因的上游调控元件。这种基因交换的结果是第二个基因的激活以及第一个基因的随之失活。这种基因对基因的表达权衡提供了净适应性增益，即使第一个基因丧失的活性在选择条件下对适应性可能发挥积极作用。
