Nucleotide sequences of the Escherichia coli nagE and nagB genes: the structural genes for the N-acetylglucosamine transport protein of the bacterial phosphoenolpyruvate: sugar phosphotransferase system and for glucosamine-6-phosphate deaminase.

ABSTRACT

The genes coding for the enzymes of N-acetylglucosamine (GlcNAc) uptake and metabolism (nagA, nagB, and nagE) are located next to glutaminyl-tRNA synthetase gene (glnS) in the Escherichia coli genome. We determined the nucleotide sequence of the nagE (ptsN) gene, encoding the GlcNAc-specific enzyme II (NagE) of the phosphoenolpyruvate sugar phosphotransferase system, and the sequence of the putative nagB gene, for glucosamine-6-phosphate deaminase. S1 mapping identified the mRNA transcript for nagE, indicating that nagE might be a sole constituent of the nagE operon, and divergent transcripts which are probably of the nagB, nagA genes. An evaluation of the hydrophobic and hydrophilic properties of NagE shows characteristics of a membrane protein. Also, NagE shows homologies to lactose permease and to the glucose-specific transport protein (enzyme IIGlc), and the glucose-specific phosphoryl carrier protein (enzyme IIIGlc). The latter two homologies are particularly interesting since no enzyme III-like protein for GlcNAc transport has been reported and enzyme IINag is of similar size as the combined enzymes IIGlc plus IIIGlc. This supports the idea that these two transport and phosphorylation systems may have evolved from a common ancestral gene.