Biosynthesis of the translation machinery: identification of regulatory factors and mechanisms

许多哺乳动物与翻译器相关的蛋白质（核糖体蛋白和延伸因子）的合成在翻译水平上受到促有丝分裂和营养信号的选择性调节。相应的mRNA的特征在于存在一个独特的序列元件，称为5'末端寡嘧啶段（5' TOP），其包含翻译顺式调节元件的核心。TOP mRNA的翻译控制通过其从分裂细胞中的多聚核糖体到静止细胞中或饥饿时的亚多聚核糖体mRNP颗粒的选择性和可逆性转变来表现。然而，TOP mRNA转录的调控机制和转录因子均未明确。我们已经建立了纯化TOP基序结合因子和测试其在TOP mRNA翻译中的活性的策略。在上一个资助期获得的数据表明，TOP mRNA翻译需要积极的作用因子，以磷酸化依赖的方式结合到TOP基序。该项目的主要任务是鉴定该因子及其在TOP mRNA调控中的作用模式。

The synthesis of many mammalian proteins associated with the translational apparatus (ribosomal proteins and elongation factors) is selectively regulated at the translational level by mitogenic and nutritional signals. The corresponding mRNAs are characterized by the presence of a unique se-quence element, termed the 5' Terminal OligoPyrimidine tract (5'TOP), which comprises the core of the translational cis-regulatory element. The translational control of TOP mRNAs is manifested by their selective and reversible shift from polysomes in dividing cells into subpolysomal mRNP particles in quiescent cells or upon starvation. However, neither the mechanisms that regulate TOP mRNA trans-lation nor transacting factors involved have been identified. We have established strategies to purify TOP motif-binding factors and to test their activity in translation of TOP mRNAs. Data obtained in the previous funding period suggest that TOP mRNA translation requires positively acting factors, which bind in a phosphorylation-dependent manner to the TOP motif. The identification of this factor and its mode of action in TOP mRNA regulation is the major task of this project.