Nucleotide sequence of fruA, the gene specifying enzyme IIfru of the phosphoenolpyruvate-dependent sugar phosphotransferase system in Escherichia coli K12.

The Enzyme IIfru of the phosphoenolpyruvate- (PEP-) dependent phosphotransferase system (PTS), which catalyses the uptake of fructose and its concomitant phosphorylation to fructose 1-phosphate by Escherichia coli, is specified by a gene designated fruA. The nucleotide sequence of a 2.5 kb PvuII restriction fragment spanning fruA+, cloned on a plasmid, was determined. This fragment contained three open reading frames (ORFs) but only one complete ORF, 1689 base pairs long, which was preceded by a well-defined Shine-Dalgarno sequence and ended with a rho-independent transcription terminator. The amino acid sequence deduced from this DNA corresponds to that of a protein of 563 amino acids (57.5 kDa), which has the hydropathic profile expected of an integral membrane protein (average hydropathy = 0.40) and which is characterized by a number of well-marked hydrophobic loops that may correspond to membrane-spanning regions. There is relatively little overall homology between this protein and those of other Enzymes II of the PTS but there is considerable correspondence between the region surrounding one of the six histidine residues (His381) of Enzyme IIfru and those surrounding the particular histidines of other Enzymes II, and of HPr, known to be involved in phosphorylation. A plasmid carrying the complete fruA+ nucleotide sequence, but not that of any other functional protein, fully restored the ability of fruA mutants to grow on fructose and of extracts of fruA mutants to phosphorylate fructose, which confirms that the nucleotide sequence determined species Enzyme IIfru.

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