Regulation of Two Clusters of Nitrogenase Genes of the Cyanobacterium Anabaena

鱼腥藻蓝藻两簇固氮酶基因的调控

• 批准号: 9723754
• 负责人: Teresa Thiel
• 金额: $ 31万
• 依托单位: University of Missouri-Saint Louis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-09-01 至 2002-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9723754&HistoricalAwards=false
• 关键词: Regulation; Two; Clusters; Nitrogenase; Genes

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.

Thiel 9723754鱼腥藻属的蓝细菌已经进化出专门用于固氮的称为异形胞的细胞。一些菌株，特别是变异鱼腥藻，具有编码不同固氮酶的多个基因。在A. variabilis编码三种固氮酶：一种V依赖性固氮酶（vnf）和两种依赖于腺嘌呤的固氮酶，一种在好氧条件下起作用（nil 1），一种仅在严格厌氧条件下起作用（nif 2）。这些基因受到严格的调控;然而，关于它们的调控知之甚少，除了它可能不是通过其他固氮细菌中描述的β 54- NifA系统。因此，了解固氮酶基因调控在A。variabilis可以拓宽我们对原核基因调控机制的理解。本研究的目的是鉴定在好氧条件下在A.变量目的是1）鉴定和表征在Mo-生长的细胞中产生的控制V-固氮酶基因表达的推定阻遏物，2）鉴定推定阻遏物的DNA结合位点并确定对阻遏作用重要的核苷酸，3）鉴定和表征在铵-生长的细胞中产生的在固定氮存在下控制nif 1和vnf表达的推定阻遏物，和4）鉴定该调节蛋白的DNA结合位点。 固氮作用，即通过固氮酶将大气中的氮气转化为氨，只存在于细菌中，包括许多蓝细菌。固氮作用不仅维持这些细菌的生长，而且维持许多通过与固氮细菌结合而接受氮的植物的生长。在所有生物体中，固氮都受到严格的调节。对许多农业上重要的固氮细菌（包括蓝细菌）的氮调节知之甚少。该研究项目的主要目标是利用分子遗传学工具来了解蓝藻鱼腥藻如何控制两组基因nif 1和vnf，使这些细胞能够在不同的环境条件下固定氮。