Dissection of a circadian oscillation into discrete domains.
Dissection of a circadian oscillation into discrete domains.
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将昼夜节律振荡分解为离散域。
DOI：
10.1073/pnas.94.8.3877
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发表时间：
1997
影响因子：
11.1
通讯作者：
Dunlap,JC
中科院分区：
文献类型：
--
作者：
Merrow,MW;Garceau,NY;Dunlap,JC
神经孢子虫中的昼夜节律振荡器是一个负反馈环，主要涉及频率（frq）基因座的产物。frq编码其蛋白质产物FRQ的多种形式，其作用是抑制frq转录物的数量。在该方案中，昼夜节律周期有两个离散且可分离的步骤：负反馈本身（抑制），其中 FRQ 起作用以降低其自身转录物的水平，以及从抑制中恢复（去抑制），其中 frq 转录物水平返回到峰值量。通过将外源可调节的 frq 转基因引入 afrq 功能丧失菌株（frq9）中，我们创建了一个人工系统，在该系统中可以启动并单独跟踪昼夜节律周期中的两个单独步骤，以观察其动力学。在这些条件下，frq-FRQ 周期占据了完整昼夜节律周期的时间尺度。在此期间，FRQ对frqtranscript水平的负反馈过程是快速且高效的；它只需要 3 至 6 小时，并且可以由每个核 10 个 FRQ 分子介导，该水平甚至低于正常振荡中看到的水平。相比之下，从负反馈中恢复需要 14 至 18 小时，这是昼夜节律周期的大部分时间，在此期间新FRQ 合成已停止，并且现有 FRQ 逐渐进行翻译后修饰。完成这两个步骤所需的总时间与观察到的正常昼夜节律周期的 22 小时周期长度非常一致。
The circadian oscillator inNeurosporais a negative feedback loop involving as principal players the products of thefrequency(frq) locus.frqencodes multiple forms of its protein product FRQ, which act to depress the amounts offrqtranscript. In this scheme there are two discrete and separable steps to the circadian cycle, negative feedback itself (repression) in which FRQ acts to decrease the levels of its own transcript, and recovery from repression (derepression) in whichfrqtranscript levels return to peak amounts. By introducing an exogenously regulatablefrqtransgene into afrqloss-of-function strain (frq9), we created an artificial system in which the two separate steps in the circadian cycle can be initiated and followed separately for purposes of observing their kinetics. Under these conditions thefrq-FRQ cycle occupies the time scale of a full circadian cycle. During this time, the process of negative feedback of FRQ onfrqtranscript levels is rapid and efficient; it requires only 3 to 6 h and can be mediated by on the order of 10 molecules of FRQ per nucleus, a level even less than that seen in the normal oscillation. In contrast, recovery from negative feedback requires 14 to 18 h, most of the circadian cycle, during which timede novoFRQ synthesis has stopped, and existing FRQ is progressively posttranslationally modified. Altogether the time required to complete both of these steps is in good agreement with the 22-h observed period length of the normal circadian cycle.