Heintzen C, Nater M, Apel K, Staiger D
Institute for Plant Sciences, Eidgenössiche Technische Hochschule, CH-8092 Zurich, Switzerland.
Proc Natl Acad Sci U S A. 1997 Aug 5;94(16):8515-20. doi: 10.1073/pnas.94.16.8515.
The endogenous clock that drives circadian rhythms is thought to communicate temporal information within the cell via cycling downstream transcripts. A transcript encoding a glycine-rich RNA-binding protein, Atgrp7, in Arabidopsis thaliana undergoes circadian oscillations with peak levels in the evening. The AtGRP7 protein also cycles with a time delay so that Atgrp7 transcript levels decline when the AtGRP7 protein accumulates to high levels. After AtGRP7 protein concentration has fallen to trough levels, Atgrp7 transcript starts to reaccumulate. Overexpression of AtGRP7 in transgenic Arabidopsis plants severely depresses cycling of the endogenous Atgrp7 transcript. These data establish both transcript and protein as components of a negative feedback circuit capable of generating a stable oscillation. AtGRP7 overexpression also depresses the oscillation of the circadian-regulated transcript encoding the related RNA-binding protein AtGRP8 but does not affect the oscillation of transcripts such as cab or catalase mRNAs. We propose that the AtGRP7 autoregulatory loop represents a "slave" oscillator in Arabidopsis that receives temporal information from a central "master" oscillator, conserves the rhythmicity by negative feedback, and transduces it to the output pathway by regulating a subset of clock-controlled transcripts.
驱动昼夜节律的内源性生物钟被认为是通过下游循环转录本在细胞内传递时间信息。拟南芥中一个编码富含甘氨酸的RNA结合蛋白Atgrp7的转录本会经历昼夜振荡，在傍晚达到峰值水平。AtGRP7蛋白也会循环，但有时间延迟，以至于当AtGRP7蛋白积累到高水平时，Atgrp7转录本水平下降。在AtGRP7蛋白浓度降至低谷水平后，Atgrp7转录本开始重新积累。在转基因拟南芥植物中过表达AtGRP7会严重抑制内源性Atgrp7转录本的循环。这些数据表明转录本和蛋白质都是能够产生稳定振荡的负反馈回路的组成部分。AtGRP7过表达也会抑制编码相关RNA结合蛋白AtGRP8的昼夜调节转录本的振荡，但不影响诸如cab或过氧化氢酶mRNA等转录本的振荡。我们提出，AtGRP7自调节环代表拟南芥中的一个“从属”振荡器，它从中央“主”振荡器接收时间信息，通过负反馈保持节律性，并通过调节一部分生物钟控制的转录本将其传递到输出途径。
