Tsang Chi Kwan, Zheng X F Steven
Department of Pharmacology and Cancer Institute of New Jersey, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
Cell Cycle. 2007 Jan 1;6(1):25-9. doi: 10.4161/cc.6.1.3675. Epub 2007 Jan 6.
Target of rapamycin (TOR) is a central component of the eukaryotic growth regulatory network. TOR controls the expression of diverse genes by all three RNA polymerases, including ribosome biogenesis, utilization and transport of nutrients, and stress-related genes. Until recently, TOR was thought to be a classical signaling kinase that regulates transcription factors in the cytoplasm. However, our recent study shows that in yeast, TOR dynamically shuttles between the cytoplasm and nucleus, and binds to 35S ribosomal DNA (rDNA) promoter. Importantly, nuclear localization and promoter-binding is crucial for TOR to control RNA polymerase (Pol) I-dependent 35S rDNA transcription. In contrast, either cytoplasmic or nuclear TOR is sufficient to regulate Pol II-dependent transcription. These observations suggest that TOR in the nucleus plays an important role in gene regulation, and that TOR takes a multifaceted approach to control expression of different genes.
雷帕霉素靶蛋白（TOR）是真核生物生长调控网络的核心组成部分。TOR通过所有三种RNA聚合酶控制多种基因的表达，包括核糖体生物合成、营养物质的利用和运输以及应激相关基因。直到最近，TOR还被认为是一种在细胞质中调节转录因子的经典信号激酶。然而，我们最近的研究表明，在酵母中，TOR在细胞质和细胞核之间动态穿梭，并与35S核糖体DNA（rDNA）启动子结合。重要的是，核定位和启动子结合对于TOR控制RNA聚合酶（Pol）I依赖的35S rDNA转录至关重要。相比之下，细胞质或细胞核中的TOR都足以调节Pol II依赖的转录。这些观察结果表明，细胞核中的TOR在基因调控中起重要作用，并且TOR采取多方面的方法来控制不同基因的表达。
