Summary: The gene encodes a product necessary for the synthesis of the iron-chelating and transport molecule enterobactin (Ent); cells harbouring mutations fail to grow in iron-deficient environments. For unknown reasons, it has not been possible to identify the product. The nucleotide sequence of the region has now been determined. An open reading frame extending in the same direction as the adjacent gene and capable of encoding an approximately 24 kDa polypeptide was found; it contained a high percentage of rare codons and two possible translational start sites. Complementation data suggested that EntD proteins truncated at the carboxy terminus retain some activity. Two REP sequences were present upstream of and an IS/56 sequence was observed downstream. RNA dot-blot hybridizations demonstrated that is transcribed from the strand predicted by the sequencing results. An recombinant plasmid was constructed and shown to express low amounts of a fusion protein of the anticipated size (approximately 125 kDa). The evidence suggests a number of possible explanations for difficulties in detecting the product. Sequence data indicate that if has its own promoter, it is weak; the REP sequences suggest that mRNA may be destabilized; and translation may be slow because of the frequency of rare codons and a possible unusual start codon (UUG). The data are also consistent with previous evidence that the product is unstable.


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