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