Regulation of gene expression: two systems

Abstract

Regulatory studies of the two diametrically opposed metabolic processes, anabolism and catabolism, are represented respectively, in an inquiry inot pyrimidine biosynthesis, as affected by repressing metabolites in Salmonella typhimurium, and in an investigation of lactose catabolism (lac operon), as affected by cAMP and a phosphotriester of cAMP in Escherichia coli. Specifically, the repressive effects of exogenous cytidine on growing S. typhimurium cells was examined in a specially constructed strain in which the pool sized of endogenous uridine 5'-diphosphate (UDP) and uridine 5'-triphosphate (UTP) cannont be varied by the addition of uracil and/or uridine to the medium. Five enzymes of the pyrimidine biosynthetic pathway and one enzyme of the arginine biosynthetic pathway were assayed from cells grown under a variety of conditions. Cystidine repressed the synthesis of dihydroorotase (encoded by...), dihydroorotate dehydrogenase (encoded by pyrD) and ornithine transcarbamylase (encoded by urgI).