Pseudouridylate Synthetase of Escherichia coli: a Catabolite-Repressible Enzyme

The growth on pseudouridine of two pyrimidine auxotrophs of Escherichia coli (Bu(-) and W63-86) was markedly enhanced when glycerol replaced glucose as a carbon source or when adenosine 3':5'-cyclic monophosphoric acid was added to medium containing glucose. These results indicated that an enzyme catalyzing a reaction in the pathway of pseudouridine conversion to uracil was sensitive to catabolite repression. The following pathway is proposed for pseudouridine utilization: [Formula: see text] [Formula: see text] Pseudouridylate synthetase was sensitive to catabolite repression in strains Bu(-) and W63-86. In contrast, strains B5RU and W5RU, mutants of Bu(-) and W63-86 which were selected for their ability to grow rapidly on pseudouridine in the presence of glucose, had high levels of pseudouridylate synthetase in the presence of glucose. In the case of B5RU but not W5RU, synthetase activity was greater in cells grown on glycerol or on glucose plus adenosine 3':5-cyclic monophosphoric acid than on glucose.