REGULATION OF PYRIMIDINE GENE EXPRESSION IN BACTERIA

本提案的目的是了解这些机制 在大肠杆菌中调控嘧啶基因的表达。在这 细菌，所有嘧啶的前体UMP的从头合成 核苷酸是由六个非连锁基因编码的六种酶催化的 和小操纵子：carAB、pyrBI、pyrC、pyrD、pyre和pyrF。这个 这些基因和操纵子的表达是由 细胞内尿苷或胞苷核苷酸的水平。近期 研究表明，PYRBI和PYRE的表达主要受调控 通过一种衰减控制机制，其中转录终止 在紧接在Rho独立的终结器(衰减器)之前 PYR结构基因(S)受UTP- 前导区内的敏感转录和偶联翻译 衰减器的上游。目前，人们对此知之甚少 其他嘧啶基因表达的调控机制。 在这项研究中，实验旨在确定新的监管 元素，并测试可能的嘧啶调节模型 基因表达。拟议的研究将集中在pyrbi操纵子上。 以及pyrC和pyrF基因。计划进行实验，以完成 关键调控元件的遗传和生化特征 参与了对pyrBI表达的衰减控制，包括 核苷酸(UTP和GTP)特异性转录暂停。菌株 表现出改变的衰减控制将被隔离，并且应该 提供各种有趣的突变，包括rpo突变。 它将被用来表征RNA的基本性质 聚合酶。对pyrBI表达的非衰减剂调节， 对嘧啶介导的血管紧张素转换酶 这部歌剧，也会被刻画出来。特别值得关注的是 UTP敏感的流产转录可能参与其中 非衰减器独立调节的启动。最近的结果表明 通过一种新的衰减控制来调节PYRC的表达 Rho依赖的转录终止机制 PyrC结构基因中的除草剂受以下因素控制 将转录和翻译结合起来。计划进行实验，以测试 Rho突变和突变对PyrC发生率的影响 PyrC表达调控的翻译启动。在……里面 此外，由PURR编码的嘌呤抑制物的可能作用 基因，在调节PYRC、PYRD和CAR AB的表达时会 检查过了。剩下的实验将检验这一机制。 调节pyrF的表达。反式-核糖核酸可能的调节作用 作用因素、流产启动和ORF基因(第二基因 在PirrF-Orff操纵子中)。

The objective of the present proposal is to understand the mechanisms regulating pyrimidine gene expression in Escherichia coli. In this bacterium, the de novo synthesis of UMP, the precursor of all pyrimidine nucleotides is catalyzed by six enzymes encoded by six unlinked genes and small operons: carAB, pyrBI, pyrC, pyrD, pyrE, and pyrF. The expression of these genes and operons is noncoordinately regulated by the intracellular levels of uridine or cytidine nucleotides. Recent studies have shown that pyrBI and pyrE expression is regulated primarily by an attenuation control mechanism in which transcriptional termination at a Rho-independent terminator (attenuator) immediately preceding the pyr structural gene(s) is regulated by the relative rates of UTP- sensitive transcription and coupled translation within a leader region upstream of the attenuator. At present, little is known about the mechanisms regulating the expression of the other pyrimidine genes. In this study experiments are designed to identify new regulatory elements and to test possible models for the regulation of pyrimidine gene expression. The proposed research will focus on the pyrBI operon and the pyrC and pyrF genes. Experiments are planned to complete the genetic and biochemical characterization of key regulatory elements involved in attenuation control of pyrBI expression, including nucleotide (UTP and GTP)specific transcriptional pausing. Strains exhibiting altered attenuation control will be isolated and should provide a variety of interesting mutations, including rpo mutations which will be used to characterize fundamental properties of RNA polymerase. Attenuator-independent regulation of pyrBI expression, which significantly contributes to the pyrimidine-mediated control of this operon, also will be characterized. Of particular interest is the possible involvement of UTP-sensitive abortive transcriptional initiation in attenuator-independent regulation. Recent results suggest that pyrC expression is regulated by a novel attenuation control mechanism in which transcriptional termination at a Rho-dependent erminator within the pyrC structural gene is controlled by the extent of coupled transcription and translation. Experiments are planned to test the effect of rho mutations and mutations that alter the rate of pyrC translational initiation on the regulation of pyrC expression. In addition, the possible role of the purine repressor, encoded by the purR gene, in the regulation of pyrC, pyrD, and car AB expression will be examined. The remaining experiments outlined will examine the mechanism regulating pyrF expression. The possible regulatory roles of trans- acting factors, abortive initiation, and the orF gene (the second gene in the pyrF-orfF operon) will be explored.