High-affinity l-arabinose transport operon : Nucleotide sequence and analysis of gene products

The nucleotide sequence of the “high-affinity” l-arabinose transport operon has been determined 3′ from the regulatory region and found to contain three open reading frames designated araF, araG and araH. The first gene 3′ to the regulatory region, araF, encodes the 23-residue signal peptide and the 306-residue mature form of the l-arabinose binding protein (33,200 M r). The binding protein, which has been described elsewhere, is hydrophilic, soluble and found in the periplasm of Escherichia coli. This gene is followed by an intragenic space of 72 nucleotides, which contains a region of dyad symmetry 23 nucleotides long capable of forming an 11-member stem-loop. The second gene, designated araG, contains an open reading frame capable of encoding an equally hydrophilic protein containing 504 residues (55,000 M r). Following a 14-nucleotide spacer, which does not appear to have any secondary structure, the third open reading frame, herein designated araH, is capable of encoding a hydrophobic protein containing 329 residues (34,000 M r) that can only be envisioned as having an integral membrane location. 3′ to araH there is a T-rich region containing a 24-nucleotide area of dyad symmetry centered 55 nucleotides from the termination codon. Analysis of the derived primary sequences of the araG and araH products indicates the nature and potential features of these components. The araG protein was found to possess internal homology between its amino and carboxyl-terminal halves, suggesting a common origin. The araG gene product has been shown to be homologous to the rbsA gene product, the hisP product, the ptsB product and the malK product, all of which presumably play similar roles in their respective transport systems. Putative ATP binding sites are observed within the regions of homology. The araH gene product has been shown to be homologous to the rbsC gene product, which is the first observed homology between two purported membrane proteins.