ORGANIZATION AND REGULATION OF THE ATCASE CISTRONS

本研究的目的是了解发展的 参与代谢途径的综合调控逻辑， 一致的，但对环境敏感的活动。 两个最 代谢调节的常见基本模式包括控制 基因表达和酶活性的生化调节 已经在细胞中产生了。 经典的互动 这两个系统正在审查的控制， 大肠杆菌嘧啶代谢与精氨酸代谢相互关系 杆菌 控制这些必需的生物合成的关键酶 途径是天冬氨酸转氨甲酰酶（ATCase），它具有调节 在氨甲酰磷酸代谢通量重新进入 精氨酸或嘧啶核苷酸的生物合成。 而E. 大肠杆菌系统提供了最复杂的综合控制模型， 另一种重要的调节模式是以进化的方式发展起来的 其中各个酶促步骤被同化成 在紧凑的建筑单元内的多功能生化步骤。 在集中注意结构组织和管理的同时， pyrLBIX操纵子在E.这个研究项目对比了这个系统 随着不同的结构组织和相关的监管变化， 在高等生物（酵母、粘阿米巴、植物和仓鼠）中观察到， 为了进一步了解的变构调节， 天冬氨酸转氨甲酰酶由于广泛的化学、突变和 晶体学数据是可用的。 此外，可以形成 活性杂交基因系统，通过交换离散的基因盒， 功能和结构上不同的酶系统， 与大肠杆菌酶有关。 这些研究表明， 是保守的遗传模块， 与AA“通过盒改组的模块化进化”一致。 有 四个重叠的遗传机制，影响的表达， pyrLBIX操纵子（减弱、翻译阻断、天然启动子 访问和RNA聚合酶对内源性核苷酸库的反应。 在 此外，pyrX顺反子编码一种蛋白质， 与调节和催化多肽的顺反子一起表达 关于ATCase 这种蛋白质的用途尚不清楚，但它已经被 纯化，并与一些单克隆抗体具有免疫交叉同一性， 抗ATCase催化链的抗体。 机械细节 将检查该系统的生理意义， 这些控制将被集成到一个详细的了解， 通过关键的嘧啶调节酶的代谢通量， 精氨酸生物合成

This research is oriented toward understanding the development of the integrated regulatory logic involved in metabolic pathways that require consistent, yet environmentally-responsive, activity. The two most common, basic patterns of metabolic regulation involve the control of gene expression and the biochemical modulation of the activity of enzymes which have already been produced in the cell. The classic interaction of these two systems is being examined in the control of the interrelationship of pyrimidine and arginine metabolism in Escherichia coli. The pivotal enzyme in the control of these essential biosynthetic pathways is aspartate transcarbamoylase (ATCase) and it has a modulating role in the metabolic flux of carbamoyl phosphate into the de novo biosynthesis of either arginine or pyrimidine nucleotides. While the E. coli system provides the most sophisticated model of integrated controls, another pattern of regulatory importance develops in an evolutionary mode in which the individual enzymatic steps become assimilated into a multifunctional biochemical steps within a compact architectural unit. While concentrating on the structural organization and regulation of the pyrLBIX operon in E. coli, this research program contrasts this system with the divergent structural organization and related regulatory changes observed in higher organisms (yeast, myxamoeba, plants and hamster) in order to further an understanding of the allosteric regulation of aspartate transcarbamoylase since extensive chemical, mutational and crystallographic data are available. Furthermore, it is possible to form active hybrid gene systems by exchanging discrete genetic cassettes from functionally and structurally divergent enzymes systems involving or related to the E coli enzyme. These studies have indicated that there are conserved genetic modules which can be rearranged in patterns consistent with aa "modular evolution by cassette shuffling". There are four overlapping genetic mechanisms which affect the expression of the pyrLBIX operon (attenuation, translational blocking, native promoter access, and RNA polymerase response to endogenous nucleotide pools. In addition, the pyrX cistron encodes a protein which is coordinately expressed with the cistrons for the regulatory and catalytic polypeptides of ATCase. The purpose of this protein is unknown but it has been purified and has immunological cross-identity with some monoclonal antibodies against the ATCase catalytic chain. The mechanistic details of this system will be examined and the physiological significance of these controls will be integrated into a detailed understanding of the metabolic flux through the key regulating enzymes for pyrimidine and arginine biosynthesis.