The Escherichia coli enterobactin biosynthesis gene, entD: nucleotide sequence and membrane localization of its protein product

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Abstract
The nucleotide sequence of the Escherichia coli enterobactin biosynthesis gene entD has been detemined. entD specifies a predicted 23579 Dalton protein containing several helical regions, a transmembrane segment and one positively charged domain. The EntD polypeptide was overexpressed and identified in electrophoretic gels as a membrane protein. Although results of conventional membrane fractionation techniques were inconclusive, protease accessibility studies provide evidence that EntD domains are exposed on the inner leaflet of the cytoplasmic membrane. The presence of repetitive extragenic palindromic (REP) sequences within the fepA-entD intercistronic region was confirmed. Lack of a canonical promoter and an iron control region 5'' to entD, along with RNA hybridization data, suggest that an iron-regulated transcript contains both fepA and entD.