TOPOLOGY OF THE PHENYLALANINE-SPECIFIC PERMEASE OF ESCHERICHIA-COLI

The PheP protein is a high-affinity phenylalanine-specific permease of the bacterium Escherichia coli, A topological model based on sequence analysis of the putative protein in which PheP has 12 transmembrane s egments with both N and C termini located in the cytoplasm had been pr oposed (J. Pi, P. J. Wookey, and A. J. Pittard, J. Bacteriol. 173:3622 -3629, 1991), This topological model of PheP has been further examined by generating protein fusions with alkaline phosphatase. Twenty-five sandwich fusion proteins have been constructed by inserting the 'phoA gene at specific sites within the pheP gene. In general, the PhoA acti vities of the fusions support a PheP topology model consisting of 12 t ransmembrane segments with the N and C termini in the cytoplasm, Howev er, alterations to the model, affecting spans III and VI, were indicat ed by this analysis and were supported by additional site-directed mut agenesis of some of the residues involved.