An evolvant of Escherichia coli that employs the L-fucose pathway also for growth on L-galactose and D-arabinose.
An evolvant of Escherichia coli that employs the L-fucose pathway also for growth on L-galactose and D-arabinose.
复制标题
大肠杆菌的进化体，也采用 L-岩藻糖途径在 L-半乳糖和 D-阿拉伯糖上生长。
DOI：
10.1007/bf02115582
复制
发表时间：
1986
影响因子：
3.9
通讯作者：
Lin,EC
中科院分区：
文献类型：
--
作者：
Zhu,Y;Lin,EC
L-半乳糖、d-阿拉伯糖和l-岩藻糖形成具有相同立体构型的六元环。然而，只有1-岩藻糖可以作为野生型大肠杆菌K-12的唯一碳源和能源。通过对两种糖的交替选择，分离出仅能生长l-半乳糖和d-阿拉伯糖的突变体。所有三种糖均可诱导T1-岩藻糖途径。转导到含有调节和结构基因的野生型fuc+区域的突变体消除了对l-半乳糖和d-阿拉伯糖的新生长能力，而转导到fuc缺失的突变体消除了对所有三种糖的生长能力。在多拷贝质粒上引入野生型fucR+（编码fuc调节子的激活蛋白）会抑制突变体onl-半乳糖和d-阿拉伯糖的生长能力，但不会抑制onl-岩藻糖的生长能力。结果表明，突变体中激活蛋白的效应特异性被拓宽。有人提出，激活剂控制的系统的适应性反应比阻遏物控制的系统更有可能在群体中实现固定，因为响应新的代谢需求而出现的第一个变体很有可能具有改变的调节特异性。在缺乏新底物的情况下，这种变化很少或根本没有代谢负担。相比之下，负控制系统出现的第一个变体极有可能是破坏阻遏物功能的随机突变的结果。尽管负控制系统在利用新条件方面比正控制系统更具机会主义性，但由于与在不存在底物的情况下无偿组成性基因表达相关的成本，适应性变化不太可能变得固定。
l-Galactose,d-arabinose, andl-fucose form six-membered rings with identical stereoconfigurations. However, onlyl-fucose can serve as the sole carbon and energy source of wild-typeEscherichia coliK-12. A mutant that can grow onl-galactose andd-arabinose was isolated by alternate selection on the two sugars. Thel-fucose pathway became inducible by all three sugars. Transduction into the mutant of the wild-type fuc+region containing both the regulatory and structural genes abolished the novel growth abilities onl-galactose andd-arabinose, whereas transduction into the mutant of a fuc deletion abolished the growth abilities on all three sugars. Introduction of the wild-type fucR+(which encodes the activator protein for the fuc regulon) on a multicopy plasmid depressed the growth abilities of the mutant onl-galactose andd-arabinose, but not onl-fucose. The results suggest that the effector specificity of the activator protein in the mutant was broadened. It is proposed that an adaptive response of an activator-controlled system is more likely than that of a repressor-controlled system to achieve fixation in a population, because the first variant to emerge in response to a novel metabolic demand has a good chance of having an altered specificity of regulation. Such a change entails little or no metabolic liability during the absence of the novel substrate. In contrast, the first variant of a negatively controlled system to emerge has an overwhelming chance of being the result of a random mutation that destroys repressor function. Although negatively controlled systems can be more opportunistic in exploiting new conditions than positively controlled systems, an adaptive change is less likely to become fixed because of the cost associated with gratuitous constitutive gene expression in the absence of the substrate.