Circadian Programming of Gene Expression in Cyanobacteria

生物复杂性的所有级别的生物体都表现出昼夜节律，这种节律由内源生物化学振荡器控制。这些生物钟的生化性质一直难以捉摸，但已经出现的一个原理是，它们的显著特性(持久性、温度补偿和夹带)在从细菌到哺乳动物的所有观察到昼夜行为的有机体中都是保守的。这一原理鼓励了人们的希望，即生化机制也是保守的--即使不是在确切的同源性上，但至少在时钟的一般组件和组成方面是这样。在这个项目中，揭示昼夜节律振荡器机制的方法集中在最不复杂、技术上最接近的生物体，在其中已经证明了生物钟：蓝藻，聚球藻。PCC7942菌株。这种生物的技术优势是它的小基因组，很容易通过遗传操作，以及它的生物发光菌株，它提供了一个高度灵活和方便的系统来监测昼夜节律基因的表达。这个蓝藻系统为详细的分子/遗传分析和时钟研究提供了极好的工具。该项目将使用这个系统来解决生物节律性的三个方面：(I)评估蓝藻从其昼夜节律振荡器获得的适应性优势，(Ii)分析时钟基因产物在中央时钟机制中的作用，以及(Iii)振荡器控制新陈代谢途径的机制的特征。许多生理和细胞过程，包括睡眠周期、体温维持、动态平衡功能、基因表达、细胞分裂和酶活性，都受到生物钟的调节。此外，这些时钟也是计时器，用来测量植物和动物生殖过程的光周期计时中的日长。生物钟的生化机制具有基本的生物学意义；了解它可能会带来对社会许多方面有用的见解。

Organisms at all levels of biological complexity manifest circadian (daily) rhythms which are controlled by an endogenous biochemical oscillator. The biochemical nature of these biological clocks has been elusive, but one principle which has emerged is that their salient properties (persistence, temperature compensation, and entrainment) are conserved in all organisms in which circadian behavior has been observed, from bacteria to mammals. This principle has encouraged the hope that the biochemical mechanism has also been conserved- if not in exact homology, then at least in terms of the general components and composition of the clock. In this project the approach to unveiling the mechanism of circadian oscillators focuses on the least complex and most technically approachable organism in which a biological clock has been demonstrated: the cyanobacterium, Synechococcus sp. strain PCC 7942. The technical advantages of this organism are its small genome, which is easily manipulated genetically, and its bioluminescent strain, which offers a highly flexible and facile system of monitoring circadian gene expression.. This cyanobacterial system provides excellent tools for detailed molecular/genetic analyses and for clock investigations. The project will use this system to address three aspects of biological rhythmicity: (i) an assessment of the fitness advantage that cyanobacteria derive from their circadian oscillators, (ii) an analysis of the roles of clock gene products in the central clock mechanism, and (iii) characterization of the mechanism by which the oscillator controls metabolic pathways.Many physiological and cellular processes, including sleep cycles, body temperature maintenance, homeostatic functions, gene expression, cell division, and enzymatic activities, are regulated by biological clocks. In addition, these clocks are also the timers that measure the daylength in photoperiodic timing of reproductive processes in plants and animals. The biochemical mechanism of circadian clocks is of fundamental biological interest; understanding it may lead to insights which will be useful to society in many ways.