Closing the circadian negative feedback loop: FRQ-dependent clearance of WC-1 from the nucleus
Closing the circadian negative feedback loop: FRQ-dependent clearance of WC-1 from the nucleus
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DOI：
10.1101/gad.1706908
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发表时间：
2008-11-15
影响因子：
10.5
通讯作者：
Dunlap, Jay C.
中科院分区：
文献类型：
--
作者：
Hong, Christian I.;Ruoff, Peter;Dunlap, Jay C.
在粗糙脉孢菌中，转录因子WCC激活FRQ的转录。FRQ与RNA解旋酶、FRH和WCC形成同源二聚体和复合体，并移位到细胞核中使WCC失活，从而关闭了延时的负反馈环。然而，关闭这一环路的详细机制仍不完全清楚。特别是在核内，与WC-1相比，FRQ的数量较少，这造成了一个难题：核FRQ如何使较大数量的WCC失活？一种可能性是FRQ可能在磷酸化依赖的抑制中发挥催化成分的作用。然而，在电子实验中显示，化学计量的非催化结合和抑制可以产生一个稳健的振荡器，即使当核FRQ水平大大低于核WCC时，只要有依赖于FRQ的WC-1从核中清除。基于这个模型，我们可以预测并现在证明WC-1稳定循环，WC-1在没有FRQ的情况下是稳定的，FRQ和WCC之间的物理结合是关闭负反馈环所必需的。此外，与基于非催化清除的抑制模型一致，相当数量的核FRQ：WCC复合体在一天中的某些时间积累，占核WC-1的10%。
In Neurospora crassa, a transcription factor, WCC, activates the transcription of frq. FRQ forms homodimers as well as complexes with an RNA helicase, FRH, and the WCC, and translocates into the nucleus to inactivate the WCC, closing the time-delayed negative feedback loop. The detailed mechanism for closing this loop, however, remains incompletely understood. In particular within the nucleus, the low amount of FRQ compared with that of WC-1 creates a conundrum: How can the nuclear FRQ inactivate the larger amount of WCC? One possibility is that FRQ might function as a catalytic component in phosphorylation-dependent inhibition. However, in silico experiments reveal that stoichiometric noncatalytic binding and inhibition can generate a robust oscillator, even when nuclear FRQ levels are substantially lower than nuclear WCC, so long as there is FRQ-dependent clearance of WC-1 from the nucleus. Based on this model, we can predict and now demonstrate that WC-1 stability cycles, that WC-1 is stable in the absence of FRQ, and that physical binding between FRQ and WCC is essential for closure of the negative feedback loop. Moreover, and consistent with a noncatalytic clearance-based model for inhibition, appreciable amounts of the nuclear FRQ: WCC complex accumulate at some times of day, comprising as much as 10% of the nuclear WC-1.