Regulation of Two Clusters of Nitrogenase Genes of the Cyanobacterium Anabaena

鱼腥藻属的Thiel 9723754蓝藻已经进化出专门用于固氮的称为异形胞的特殊细胞。一些菌株，特别是可变鱼腥藻，有多个基因编码不同的固氮酶。在变种拟青霉中有三个基因簇编码三种固氮酶：一种依赖于V的固氮酶(VnF)和两种依赖钼的固氮酶，一种在有氧条件下起作用(Nil1)，另一种只在严格厌氧条件下起作用(Nif2)。这些基因受到严格的调控；然而，人们对它们的调控知之甚少，除了可能不是通过其他固氮菌中描述的(54-NIFA系统)。因此，了解变色拟青霉固氮酶基因调控可以拓宽我们对原核生物基因调控机制的理解。本研究的目的是确定在异形胞中在有氧条件下发挥作用的nif1和vnf基因在环境控制中的顺式元件和反式作用因子。本研究的目的是：1)鉴定和鉴定在钼培养细胞中控制V-固氮酶基因表达的抑制因子，2)鉴定抑制因子的DNA结合部位并确定对抑制作用重要的核苷酸，3)鉴定和鉴定在固定氮存在下控制nif1和VNF表达的氨基培养细胞中的抑制因子，以及4)鉴定该调节蛋白的DNA结合位点。固氮，即通过固氮酶将大气中的氮气转化为氨的过程，只存在于细菌中，包括许多蓝藻。固氮不仅维持了这些细菌的生长，而且还维持了许多植物的生长，这些植物通过与固氮菌联合来接受氮。在所有生物体中，固氮都受到严格的调控。许多农业上重要的固氮菌，包括蓝藻，对氮的调节知之甚少。这项研究的主要目标是利用分子遗传学的工具来了解蓝藻是如何控制两组基因nif1和vnf的，这两组基因允许这些细胞在不同的环境条件下固定氮。

Thiel 9723754 Cyanobacteria of the genus Anabaena have evolved specialized cells called heterocysts that function exclusively for nitrogen fixation. Some strains, notably Anabaena variabilis, have multiple genes that encode different nitrogenases. There are three clusters of genes in A. variabilis that encode three nitrogenases: a V-dependent nitrogenase (vnf) and two molybdenum-dependent nitrogenases, one that functions under aerobic conditions (nil1) and one that functions only under strictly anaerobic conditions (nif2). These genes are tightly regulated; however, very little is known about their regulation except that it is probably not via the (54- NifA system described in other nitrogen-fixing bacteria. Thus, an understanding of nitrogenase gene regulation in A. variabilis can broaden our understanding of mechanisms of procaryotic gene regulation. The goal of this research is to identify the cis elements and trans-acting factors that function in the environmental control of the nif1 and vnf genes that function under aerobic conditions in heterocysts of A. variabilis. The objectives are to 1 ) identify and characterize a putative repressor made in Mo-grown cells that controls V-nitrogenase gene expression, 2) identify the DNA-binding site for the putative repressor and determine the nucleotides that are important for repression, 3) identify and characterize a putative repressor made in ammonium-grown cells that controls nif1 and vnf expression in the presence of fixed nitrogen, and 4) identify the DNA-binding site for this regulatory protein. Nitrogen fixation, the conversion of atmospheric nitrogen gas to ammonia by the enzyme nitrogenase, is found exclusively in bacteria, including many cyanobacteria. Nitrogen fixation sustains the growth of not only these bacteria, but also of many plants that receive nitrogen by associations with nitrogen-fixing bacteria. In all organisms nitrogen fixation is tightly regulated. Very little is known about nitrogen regulation in many agriculturally impo rtant nitrogen-fixing bacteria, including the cyanobacteria. The primary objective of this research project is to use the tools of molecular genetics to understand how the cyanobacterium, Anabaena variabilis, controls two sets of genes, nif1 and vnf, that allow these cells to fix nitrogen under diverse environmental conditions.