Involvement of the Escherichia coli Phosphoenolpyruvate‐Dependent Phosphotransferase System in Regulation of Transcription of Catabolic Genes

Abstract

Synthesis of catabolite-sensitive enzymes is repressed in mutants defective in the general proteins (enzyme I and HPr) of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system (ptsl and ptsH mutations). To elucidate the mechanism of this phenomenon we constructed isogenic strains carrying pts mutations as well as different lesions of regulation of the lac operon or mutations affecting adenylate cyclase activity (cyu mutation) and synthesis of cyclic-AMP-receptor protein (crp mutation) Measurements of the differential rate of 1-galactosidase synthesis in these strains showed that the repressive effect of pts mutations was revealed in luc', l a d , luc0" and cyu bacteria, but it was lost in lucP and crp strains.It was concluded that mutational damage to the general components of the phosphoenolpyruvatedependent phosphotransferase system diminishes activity of the lac promoter.The results obtained led to the conclusion that pts gene products (apparently phospho -HPr) are necessary for the initiation of transcription of catabolite-sensitive operons in E. coli.The phosphoenolpyruvate : carbohydrate phosphotransferase system of Escherichia coli carries out the phosphorylation of many carbohydrates [ 1 -41. This process involves the activities of several protein components. Enzyme I catalyzes the transfer of the phosphoryl group from phosphoenolpyruvate to a small histidine-containing heat-stable protein HPr. The phospho -HPr generated serves as a donor of the phosphoryl moiety in the phosphotransferase reaction catalysed by the enzyme 11 which is specfic for a certain carbohydrate or its analogue. Enzyme I and HPr are designated the general proteins of the system since they are required for the phosphorylation of all sugar substrates of the phosphotransferase system. These two components are constitutive soluble proteins ; their synthesis is determined by theptsl (for enzyme I) and ptsH (for HPr) genes [3]. At present it is well established that the phosphotransferase system is necessary for the transport and metabolism of carbohydrates of D-gluco and u-munno configuration [2,4]. Transport of the sugar is catalyzed concomitantly with phosphorylation of the carbohydrate at the expense of phosphoenolpyruvate. Sugars that have an obligatory requirement for phosphorylation during transfer are called phosphotransferase sugars. Non-phosphotransferase substrates are those transported into bacterial cell via their specific systems [2].Mutational damage to the general proteins of the phosphotransferase system (ptsl, ptsI,H and ptsH mutations) leads to severe disturbance of transport of the phosphotransferase sugars into E. coli cells and these mutants are unable to grow in media containing these sugars as the sole source of carbon [5-1.51.Some properties of the p t s mutants indicate that the products of the p t s genes are relevant to the regulation of the synthesis of catabolite-sensitive enzymes. As was demonstrated in our laboratory, pts

Insensitivity of the Escherichia coli K-12 adenylate cyclase to mannose under the conditions of catabolite repression

“…The following E. coli K-12 strains were used: HfrC (met), JC8563 (met ilv), J621 (his trp strr). Growth of bacteria and/~-galactosidase assay were as in [6]. Carbohydrate (0.01 mM) utilization was studied in bacteria grown into the logarithmic phase in media containing either mannose, glucose or mannitol.…”

Competition between Two Pathways for Sugar Uptake by the Phosphoenolpyruvate‐Dependent Sugar Phosphotransferase System in Salmonella typhimurium

“…Factor IIIG1" is a soluble phosphoprotein, which transfers phosphoryl groups from phospho-HPr to the membrane-bound enzyme/1I-BG'". The activity of the glucose-specific IIIG1"/II-BG1" pathway varies with the growth conditions and is maximal if the cells are grown with glucose as a carbon source [3].In addition to its role in sugar transport, the P-pyruvate : sugar phosphotransferase system was shown to be involved in the regulation of cell metabolism [1,4]. Both the rate of synthesis of adenosine 3',5'-(cyclic) monophosphate [5 -81 and the transport of several metabolites which are not substrates of P-pyruvate : sugar phosphotransferase [1,9 -111 is Abbreviations.…”

“…In addition to its role in sugar transport, the P-pyruvate : sugar phosphotransferase system was shown to be involved in the regulation of cell metabolism [1,4]. Both the rate of synthesis of adenosine 3',5'-(cyclic) monophosphate [5 -81 and the transport of several metabolites which are not substrates of P-pyruvate : sugar phosphotransferase [1,9 -…”

Isolation and investigation of the Escherichia coli mutant with the deletion in the ptsH gene

“…These mutations lead to the abrupt decrease in phospho-HPr -a donor of the phosphoryl group in the vector reactions of carbohydrate phosphorylation catalyzed by the specific components of the PT-system [3,4]. Besides alteration of the in vitro phosphotr~~erase reaction and transport function of the PT-system, the lack of phospho+Pr leads to changes in regulation of inducible enzyme synthesis, characteristic to pts mutants [1] …”

“…The phosphoenolpyruvate (PEP): sugar phosphotransferase system (the PT-system) is known to regulate the synthesis of certain inducible enzymes [ 1,2]. The behaviour of pfs1 and prsH mutants (i.e., mutants with defective common components of the PT-system enzyme I and protein HPr) indicates that pts gene products are functional in inducible enzyme synthesis [2].…”