REGULATION OF PYRIMIDINE GENE EXPRESSION IN BACTERIA

本研究的目的是阐明其调控机制。 嘧啶基因在大肠杆菌和鼠伤寒沙门氏菌中的表达 在这些细菌中，UMP的从头合成，是ALL的前体 嘧啶核苷酸，由六种酶催化，由六种未连接的酶编码 基因和操纵子。这些基因和操纵子是不协调表达的。 并受到尿苷或胞苷的负面调节 核苷酸。所有的核苷酸效应器的精确同一性 除了pyrBI操纵子外，其他基因都是未知的。 这项研究中的实验旨在确定调节元件和 检测PYR基因表达的可能调控机制。特别的 感兴趣的是大肠杆菌的pyrBI操纵子，它编码 嘧啶生物合成酶、天冬氨酸转氨甲基酶。表达方式 该操纵子的转录水平受UTP负调控。初步研究表明 揭示了紧接在结构基因之前的衰减器 在两个pyrBI启动子的上游启动的位点转录是 有效地终止了。确定的其他功能建议为 UTP依赖转录的相对速率的调控 在pyrBI引线区域内和引线的耦合平移 转录控制在衰减器的转录终止。这 模型将通过体外定点突变来改变DNA进行测试 明显参与衰减控制的序列。这些因素的影响 调节的突变将在体内进行研究。附加PYRBI 调节性突变将在体内分离并鉴定。 影响衰减频率的生理和遗传因素 并将检查通读转录。研究也包括在内。 在大肠杆菌中表达了pyrC和pyrF。初步研究表明， 尿苷负性调节的pyrF表达 核苷酸，可能不受衰减机制的控制。这些 研究将会延长。调节性DNA的可能参与 本课程将探讨约束因素。PyrC基因被包括在一个 代表由胞苷调控的PYR基因 核苷酸。描述了识别衰减特征的研究 控制和其他类型的控制机制。UTP、CTP和 PpGpp对pyrC和pyrF表达的影响将在体外测定 依赖DNA的转录-翻译耦合系统。

The purpose of this research is to elucidate the mechanisms regulating pyrimidine gene expression in Escherichia coli and Salmonella typhimurium. In these bacteria, the de novo synthesis of UMP, the precursor of all pyrimidine nucleotides, is catalyzed by six enzymes encoded by six unlinked genes and operons. These genes and operons are expressed noncoordinately and are subject to negative regulation by either a uridine or cytidine nucleotide. The exact identities of the nucleotide effectors for all the genes except the pyrBI operon are unknown. Experiments in this study are designed to identify regulatory elements and to test possible control mechanisms of pyr gene expression. Of particular interest is the pyrBI operon of E. coli, which encodes the subunits of the pyrimidine biosynthetic enzyme aspartate transcarbamylase. The expression of this operon is negatively regulated by UTP. Initial studies have revealed an attenuator immediately preceding the structural genes at which site transcription initiated upstream at either of two pyrBI promoters is efficiently terminated. Additional features identified suggest a model for regulation in which the relative rates of UTP-dependent transcription within the pyrBI leader region and coupled translation of the leader transcript control transcriptional termination at the attenuator. This model will be tested by in vitro site-directed mutagenesis to alter DNA sequences apparently involved in attenuation control. The effects of these mutations on regulation will be studied in vivo. Additional pyrBI regulatory mutations will be isolated in vivo and characterized. Physiological and genetic factors influencing the frequency of attenuated and readthrough transcription will be examined. Also included are studies of pyrC and pyrF expression in E. coli. Preliminary studies indicate that pyrF expression, which also is negatively regulated by a uridine nucleotide, may not be controlled by an attenuation mechanism. These studies will be extended. The possible involvement of a regulatory DNA binding factor will be explored. The pyrC gene is included as a representative of the pyr genes that are regulated by a cytidine nucleotide. Studies are described to identify features of attenuation control and other types of control mechanisms. The effect of UTP, CTP, and ppGpp on pyrC and pyrF expression will be measured in an in vitro DNA-dependent, coupled transcription-translation system.