RUI: Regulation of Nitrogenases in the Cyanobacterium Anabaena Variabilis

丝状蓝藻是一种独特的微生物，可以通过植物型光合作用产生能量，并通过固氮来减少大气中的氮。光合作用产生的氧气严重抑制固氮作用；因此，这两个不相容的代谢过程在空间上是分开的。光合作用发生在营养细胞中，固氮发生在异囊中。异囊是由于对固定氮的缺乏而在细丝中以半规则模式产生的终末分化细胞。氮酶是一种酶复合物，位于异囊中，负责将大气中的氮还原为氨。PI对控制杂种囊中氮酶基因表达的调控信号感兴趣。她最近发现了一组新的基因，这些基因似乎可以编码变异性水藻（Anabaena variabilis）中的第二种氮酶。第二种氮酶在遗传上与两种固氮细菌中的钒依赖氮酶相似。它似乎不是水藻常规氮酶的另一个副本。本课题拟通过对变水藻（Anabaena variabilis）的两个氮酶基因进行分析，试图找出在发育过程中调控氮酶表达的重要调控位点和调控基因。

Filamentous cyanobacteria are unique microorganisms which can produce energy by plant type photosynthesis and reduce atmospheric nitrogen by nitrogen fixation. Nitrogen fixation is severely inhibited by the oxygen produced by photosynthesis; hence, these two incompatible metabolic processes are spatially separated. Photosynthesis occurs in vegetative cells and nitrogen fixation occurs in heterocysts. Heterocysts are terminally differentiated cells which arise in a semi-regular pattern in a filament in response to starvation for fixed nitrogen. Nitrogenase is the enzyme complex, localized in heterocysts, that is responsible for the reduction of atmospheric nitrogen to ammonia. The PI is interested in the regulatory signals which control expression of nitrogenase genes in heterocysts. She has recently found a new set of genes that appear to code for a second nitrogenase in Anabaena variabilis. This second nitrogenase is genetically similar to a vanadium- dependent nitrogenase characterized in two species of Azotobacter. It does not appear to be another copy of the conventional nitrogenase of Anabaena. The PI proposes to analyze the two nitrogenase genes of Anabaena variabilis in an attempt to identify regulatory sites and regulatory gene that are important in developmental control of expression of nitrogenases.