Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
J Biol Chem. 2010 Apr 9;285(15):11508-15. doi: 10.1074/jbc.M109.071688. Epub 2010 Feb 16.
FREQUENCY (FRQ) is the central component of the Neurospora circadian clock. All FRQ proteins form the FFC complex with FRH (FRQ-interacting RNA helicase) that acts as the negative element in the circadian negative feedback loop by repressing frq mRNA levels. To understand the function of the FRQ-FRH interaction, we mapped and identified the minimal FRQ region that is required for FRQ-FRH interaction. We demonstrated that the FRQ-FRH complex formation is required for the interaction between FRQ and the White Collar Complex (WCC) and clock function. On the other hand, in the FRQ-FRH complex, FRQ is also required for the FRH-WCC interaction. Disruption of FRQ-FRH interaction or down-regulation of FRH results in hypophosphorylation, rapid degradation of FRQ, as well as low levels of WHITE COLLAR-1 and WHITE COLLAR-2. Furthermore, we showed that the rapid FRQ degradation in the absence of FRH is independent of FWD-1, the ubiquitin E3 ligase of FRQ under normal conditions, thus uncovering an alternative pathway for FRQ degradation.
频率（FRQ）是 Neurospora 生物钟的核心组成部分。所有 FRQ 蛋白与 FRH（FRQ 相互作用 RNA 解旋酶）形成 FFC 复合物，该复合物作为生物钟负反馈回路中的负元件，通过抑制 frq mRNA 水平来发挥作用。为了了解 FRQ-FRH 相互作用的功能，我们对 FRQ-FRH 相互作用所需的最小 FRQ 区域进行了作图和鉴定。我们证明了 FRQ-FRH 复合物的形成对于 FRQ 与 White Collar Complex（WCC）之间的相互作用和时钟功能是必需的。另一方面，在 FRQ-FRH 复合物中，FRQ 也需要与 FRH-WCC 相互作用。FRQ-FRH 相互作用的破坏或 FRH 的下调导致 FRQ 的低磷酸化、快速降解，以及 WHITE COLLAR-1 和 WHITE COLLAR-2 的水平降低。此外，我们还表明，在没有 FRH 的情况下，FRQ 的快速降解不依赖于 FWD-1，即正常条件下 FRQ 的泛素 E3 连接酶，从而揭示了 FRQ 降解的另一种途径。
