The mannose-permease of the bacterial phosphotransferase system. Gene cloning and purification of the enzyme IIMan/IIIMan complex of Escherichia coli

Abstract

The mannose-permease complex of the phosphoenolpyruvate-dependent phosphotranferase system exhibits two apparently unrelated activities. It mediates active transport concomitant with phosphorylation of mannose, 2-deoxyglucose, and a number of other hexoses, and it is required for penetration of bacteriophage lambda DNA across the cytoplasmic membrane of Escherichia coli. A cloned fragment of E. coli chromosome restores mannose-fermentation in, and confers lambda sensitivity to, an E. coli strain with a mutation in the gene for the phosphoenolpyruvate-dependent mannose uptake. Using complementation analysis of phosphotransferase activity and of lambda sensitivity, a 3.8-kilobase pair fragment was shown to carry two adjacent genes, ptsM and ptsL. Although each gene has a promoter of its own, transcription of ptsL has a positive polar effect on the transcription of ptsM. A complex of two proteins, IIMan and IIIMan, was purified to homogeneity from an overproducing strain. IIMan is encoded by gene ptsM, IIIMan by gene ptsL. IIMan, a 27-kDa protein, is the transmembrane component of the complex. IIIMan, a 35-kDa protein, exists as a dimer and is found both membrane-associated and free in the cytoplasm. IIIMan can be phosphorylated in a phosphoenolpyruvate-dependent reaction, while phosphorylation of IIMan could not be detected. IIMan and IIIMan are both required for phosphorylation of 2-deoxyglucose in vitro, while IIMan alone is sufficient to confer lambda sensitivity.