Spontaneous point mutations that occur more often when advantageous than when neutral.
Spontaneous point mutations that occur more often when advantageous than when neutral.
复制标题
自发点突变在有利时比中性时更常发生。
DOI：
10.1093/genetics/126.1.5
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发表时间：
1990
期刊：
影响因子：
3.3
通讯作者：
Hall,BG
中科院分区：
文献类型：
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作者：
Hall,BG
最近的报告对“突变不断出现而不考虑其效用”（用J.凯恩斯的话来说）的普遍看法提出了质疑，并提出一些突变（凯恩斯称之为“定向”突变）可能是对环境挑战的特定反应，即，它们可能在有利时比在中立时更频繁地发生。本文表明，当回复是有利的时，在长期色氨酸剥夺的条件下，trp操纵子中的点突变回复为trp+的频率比当回复是中性时在存在色氨酸的情况下更高。总的突变率，从突变率测定缬氨酸抗性和紫胶操纵子的组成型表达，色氨酸饥饿期间没有增加。当细胞饥饿半胱氨酸一段类似的时间时，色氨酸回复率没有增加，表明回复率的增加是特定于回复有利的条件。对观察结果的两种人为解释进行了检测，并将其视为不太可能，即一些既存回复突变体的延迟生长和一些细胞以老化菌落中的死亡细胞为代价的隐蔽生长。色氨酸+逆转发生，而色氨酸-菌落老化的情况下，色氨酸被证明是时间依赖性的，而不是复制依赖性的，它表明，它们发生的机制不同，已被研究在生长的细胞。这种突变的分子基础的启发式模型提出了与该模型相一致的证据进行了讨论。有人建议，在这个和以前的研究结果可以解释的基础上，潜在的随机机制，在长时间的生理压力的作用，而“定向”突变不一定是这些观察的基础上。
Recent reports have called into question the widespread belief "that mutations arise continuously and without any consideration for their utility" (in the words of J. Cairns) and have suggested that some mutations (which Cairns called "directed" mutations) may occur as specific responses to environmental challenges, i.e., they may occur more often when advantageous than when neutral. In this paper it is shown that point mutations in the trp operon reverted to trp+ more frequently under conditions of prolonged tryptophan deprivation when the reversions were advantageous, than in the presence of tryptophan when the reversions were neutral. The overall mutation rate, as determined from the rates of mutation to valine resistance and to constitutive expression of the lac operon, did not increase during tryptophan starvation. The trp reversion rate did not increase when the cells were starved for cysteine for a similar period, indicating that the increased reversion rate was specific to conditions where the reversions were advantageous. Two artifactual explanations for the observations, delayed growth of some preexisting revertants and cryptic growth by some cells at the expense of dying cells within aged colonies, were tested and rejected as unlikely. The trp+ reversions that occurred while trp- colonies aged in the absence of tryptophan were shown to be time-dependent rather than replication-dependent, and it is suggested that they occur by mechanisms different from those that have been studied in growing cells. A heuristic model for the molecular basis of such mutations is proposed and evidence consistent with that model is discussed. It is suggested that the results in this and previous studies can be explained on the basis of underlying random mechanisms that act during prolonged periods of physiological stress, and that "directed" mutations are not necessarily the basis of those observations.