The effects of thymine and of phosphate deprivation on enzyme synthesis in Escherichia coli

Abstract

Abstract The ability of a thymine-requiring mutant of Escherichia coli to form the inducible enzyme β-galactosidase in media of different composition and at different stages of thymine starvation was investigated. The differential rate of synthesis of this enzyme in a medium containing casamino acids but no readily utilizable energy source, is the same whether or not protein synthesis is restricted by the omission of inorganic phosphate. Addition of a readily utilizable energy source, glycerol, reduces the differential rate of synthesis of the enzyme slightly when phosphate is present, but greatly when phosphate is absent. Apparently, catabolites derived from glycerol accumulate in the cell when the rate of protein synthesis is restricted by the lack of phosphate and repress the formation of enzymes sensitive to catabolite repression. The lack of thymine is initially without effect on the synthesis of β-galactosidase. When thymine starvation is sufficiently prolonged to cause the death of the cell, the rate of protein synthesis is reduced and glycerol almost completely represses the synthesis of β-galactosidase. The extensive thymine starvation reduces the cell's capacity to form the enzyme β-galactosidase in the absence of glycerol somewhat more than its capacity to synthesize proteins.