Balakirev Evgeniy S, Anisimova Maria, Ayala Francisco J
Department of Ecology and Evolutionary Biology, University of California, 321 Steinhaus Hall, Irvine, CA 92697-2525, USA.
J Mol Evol. 2006 Apr;62(4):496-510. doi: 10.1007/s00239-005-0140-1. Epub 2006 Mar 17.
We examine the pattern of molecular evolution of the beta-esterase gene cluster, including the Est-6 and psiEst-6 genes, in eight species of the Drosophila melanogaster subgroup. Using maximum likelihood estimates of nonsynonymous/synonymous rate ratios, we show that the majority of Est-6 sites evolves under strong (48% of sites) or moderate (50% of sites) negative selection and a minority of sites (1.5%) is under significant positive selection. Est-6 sites likely to be under positive selection are associated with increased intraspecific variability. One positively selected site is responsible for the EST-6 F/S allozyme polymorphism; the same site is responsible for the EST-6 functional divergence between species of the melanogaster subgroup. For psiEst-6 83.7% sites evolve under negative selection, 16% sites evolve neutrally, and 0.3% sites are under positive selection. The positively selected sites of psiEst-6 are located at the beginning and at the end of the gene, where there is reduced divergence between D. melanogaster and D. simulans; these regions of psiEst-6 could be involved in regulation or some other function. Branch-site-specific analysis shows that the evolution of the melanogaster subgroup underwent episodic positive selection. Collating the present data with previous results for the beta-esterase genes, we propose that positive and negative selection are involved in a complex relationship that may be typical of the divergence of duplicate genes as one or both duplicates evolve a new function.
我们研究了黑腹果蝇亚组八个物种中β-酯酶基因簇（包括Est-6和psiEst-6基因）的分子进化模式。通过非同义/同义率比的最大似然估计，我们发现大多数Est-6位点在强负选择（48%的位点）或中度负选择（50%的位点）下进化，少数位点（1.5%）处于显著正选择之下。可能处于正选择下的Est-6位点与种内变异性增加有关。一个正选择位点导致了EST-6 F/S同工酶多态性；同一个位点导致了黑腹果蝇亚组物种间EST-6的功能差异。对于psiEst-6，83.7%的位点在负选择下进化，16%的位点中性进化，0.3%的位点处于正选择之下。psiEst-6的正选择位点位于基因的起始和末端，在黑腹果蝇和拟果蝇之间这些区域的差异较小；psiEst-6的这些区域可能参与调控或其他功能。分支位点特异性分析表明，黑腹果蝇亚组的进化经历了间歇性正选择。将目前的数据与之前关于β-酯酶基因的结果进行整理，我们提出正选择和负选择参与了一种复杂的关系，这可能是重复基因在一个或两个重复基因进化出新功能时分歧的典型特征。
