Nucleotide sequence of the phoM region of Escherichia coli: four open reading frames may constitute an operon

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Abstract
The phoM gene is one of the positive regulatory genes for the phosphate regulon of Escherichia coli. We analyzed the nucleotide sequence of a 4.7-kilobase chromosomal DNA segment that encompasses the phoM gene and its flanking regions. Four open reading frames (ORFs) were identified in the order ORF1-ORF2-ORF3 (phoM)-ORF4-dye clockwise on the standard E. coli genetic map. Since these ORFs are preceded by a putative promotor sequence upstream of ORF1 and followed by a putative terminator distal to ORF4, they seem to constitute an operon. The 157-amino-acid ORF1 protein contains highly hydrophobic amino acids in the amino-terminal portion, which is a characteristic of a signal peptide. The 229-amino-acid ORF2 protein is highly homologous to the PhoB protein, a positive regulatory protein for the phosphate regulon. The ORF3 (phoM gene) protein contains two stretches of highly hydrophobic residues in the amino-terminal and central regions and, therefore, may be a membrane protein. The 450-amino-acid ORF4 protein contains long hydrophobic regions and is likely to be a membrane protein.