Cheng Ping, He Qun, He Qiyang, Wang Lixin, Liu Yi
Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Genes Dev. 2005 Jan 15;19(2):234-41. doi: 10.1101/gad.1266805. Epub 2004 Dec 29.
The eukaryotic circadian oscillators consist of autoregulatory negative-feedback loops. FRQ, WC-1, and WC-2 are three known components of the negative-feedback loop of the Neurospora circadian oscillator. FRQ represses its own transcription by interacting with the WC-1/WC-2 complex and inhibiting WC's role in transcriptional activation. Here we show that all FRQ associates with FRH, an essential DEAD box-containing RNA helicase in Neurospora. The budding yeast homolog of FRH, Dob1p/Mtr4p, is a cofactor of exosome, an important regulator of RNA metabolism in eukaryotes. Down-regulation of FRH by inducible expression of a hairpin RNA leads to low levels of FRQ but high levels of frq RNA and the abolishment of circadian rhythmicities. FRH is associated with the WC complex and this interaction is maintained in a frq null strain. Disruption of the FRQ-FRH complex by deleting a domain in FRQ eliminates the FRQ-WC interaction, suggesting that FRH mediates the interaction between FRQ and the WC complex. These data demonstrate that FRH is an essential component in the circadian negative-feedback loop and reveal an unexpected role of an RNA helicase in regulating gene transcription.
真核生物钟振荡器由自动调节的负反馈环组成。FRQ、WC-1和WC-2是粗糙脉孢菌生物钟振荡器负反馈环的三个已知组成部分。FRQ通过与WC-1/WC-2复合物相互作用并抑制WC在转录激活中的作用来抑制其自身的转录。在此我们表明，所有的FRQ都与FRH相关联，FRH是粗糙脉孢菌中一种必需的含DEAD盒的RNA解旋酶。FRH在芽殖酵母中的同源物Dob1p/Mtr4p是外泌体的一个辅助因子，外泌体是真核生物中RNA代谢的重要调节因子。通过诱导表达发夹RNA来下调FRH会导致FRQ水平降低，但frq RNA水平升高以及昼夜节律性消失。FRH与WC复合物相关联，并且这种相互作用在frq缺失菌株中得以维持。通过删除FRQ中的一个结构域来破坏FRQ-FRH复合物会消除FRQ-WC相互作用，这表明FRH介导了FRQ与WC复合物之间的相互作用。这些数据表明FRH是生物钟负反馈环中的一个必需组成部分，并揭示了一种RNA解旋酶在调节基因转录中的意想不到的作用。
