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Promoter-Like Mutation Affecting HPr and Enzyme I of the Phosphoenolpyruvate:Sugar Phosphotransferase System in Salmonella typhimurium¹

^a Department of Biology and The McCollum-Pratt Institute, The Johns Hopkins University, Baltimore, Maryland 21218

ABSTRACT

A promoter-like mutation, ptsP160, has been identified which drastically reduces expression of the genes specifying two proteins, HPr and enzyme I, of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) in Salmonella typhimurium. This mutation lies between trzA, a gene specifying susceptibility to 1,2,4-triazole, and ptsH, the structural gene for HPr. It leads to a loss of active transport of those sugars that require the PTS for entry into the cell. Pseudorevertants of strains carrying this promoter-like mutation have additional lesions very closely linked to ptsP160 by transduction analysis and are noninducible for HPr and enzyme I above a basal level. Presumably, strains carrying ptsP160 are defective in the normal induction mechanism for HPr and enzyme I, and the pseudorevertants derived from them result from second-site initiation signals within or near this promoter-like element. The induction of HPr and enzyme I above their noninduced levels apparently is not required for transport of at least one PTS sugar, methyl -D-glucopyranoside, since this sugar is taken up by the pseudorevertants at the same rate as by the wild type. The existence of a promoter-like element governing the coordinate inducibility of both HPr and enzyme I suggests that ptsH and ptsI constitute an operon. Wild-type levels of a sugar-specific PTS protein, factor III, are synthesized in response to the crr⁺ gene in both a ptsP160 strain and its pseudorevertants; this suggests that the crr⁺ gene has its own promoter distinct from ptsP.

² Present address: The University of California at Berkeley, Department of Molecular Biology, Berkeley, Calif. 94720.

³ Present address: The University of Maryland, School of Medicine, Baltimore, Md. 21201.

⁴ Present address: Eye Pathology Laboratory, Wilmer Ophthalmological Institute, The Johns Hopkins Hospital, Baltimore, Md. 21205.

¹ Contribution no. 792 from the McCollum-Pratt Institute of the Johns Hopkins University.