Adaptive Mutations in RNA Polymerase and the Transcriptional Terminator Rho Have Similar Effects on Escherichia coli Gene Expression
Adaptive Mutations in RNA Polymerase and the Transcriptional Terminator Rho Have Similar Effects on Escherichia coli Gene Expression
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DOI：
10.1093/molbev/msx216
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发表时间：
2017-11-01
影响因子：
10.7
通讯作者：
Gaut, Brandon S.
中科院分区：
文献类型：
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作者：
Gonzalez-Gonzalez, Andrea;Hug, Shaun M.;Gaut, Brandon S.
转录调控因子的修饰在适应中起着重要作用。在这里，我们比较了大肠杆菌rpoB（编码RNA聚合酶β亚基的基因）和rho（编码转录终止子的基因）内部和之间多个有益突变的影响。这两个基因在许多大肠杆菌进化实验中都有适应性突变，但在我们之前的大规模热应激实验中，这两个基因表现出不同的适应途径。为了比较有益突变的影响，我们在两个基因中分别设计了四个有利突变，并测量了它们在42.2℃下对适应度、生长、基因表达和转录终止的影响。在8个突变中，两个rho突变对相对适应度没有可检测到的影响，这表明它们仅在上位相互作用的背景下是有益的。剩下的6个突变的平均相对适应性收益接近20%。rpoB突变影响了近1700个基因的表达；rho突变影响较少基因的表达，但大多数（83%）是rpoB突变改变的基因的一个子集。在8个突变体中，相对适应度与突变将基因表达恢复到37.0摄氏度的非应激状态的程度相关。两个基因的有益突变对适应度、生长或基因表达的影响并不相同，但它们对基因表达和全基因组转录终止产生平行的表型效应。
Modifications to transcriptional regulators play a major role in adaptation. Here, we compared the effects of multiple beneficial mutations within and between Escherichia coli rpoB, the gene encoding the RNA polymerase beta subunit, and rho, which encodes a transcriptional terminator. These two genes have harbored adaptive mutations in numerous E. coli evolution experiments but particularly in our previous large-scale thermal stress experiment, where the two genes characterized alternative adaptive pathways. To compare the effects of beneficial mutations, we engineered four advantageous mutations into each of the two genes and measured their effects on fitness, growth, gene expression and transcriptional termination at 42.2 degrees C. Among the eight mutations, two rho mutations had no detectable effect on relative fitness, suggesting they were beneficial only in the context of epistatic interactions. The remaining six mutations had an average relative fitness benefit of similar to 20%. The rpoB mutations affected the expression of similar to 1,700 genes; rho mutations affected the expression of fewer genes but most (83%) were a subset of those altered by rpoB mutants. Across the eight mutants, relative fitness correlated with the degree to which a mutation restored gene expression back to the unstressed, 37.0 degrees C state. The beneficial mutations in the two genes did not have identical effects on fitness, growth or gene expression, but they caused parallel phenotypic effects on gene expression and genome-wide transcriptional termination.