Nucleotide sequence of thehemClocus encoding porpbobilinogen deaminase ofEscherichia coliK12

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Abstract
Porphobilinogen deaminase, the product of the hemC locus in Escherichia coli K12, catalyses the tetrapolymerisation of porphobilinogen (PBG) into the hydroxymethylbilane, preuroporphyrinogen. The hemC locus has been subcloned from the Clarke and Carbon plasmid pLC41–4. The sequence of the hemC structural gene and flanking DNA was determined by the dideoxy chain termination method of Sanger. The structural gene for hemC is located within a 942bp sequence encoding the monomeric PBG deaminase, molecular weight 33,857. The extent of the coding region was confirmed by sequencing the N-terminus of the purified enzyme and by determination of the molecular weight. The hemC locus is closely linked to the cyaA locus, the genes being transcribed in a divergent manner. Upstream of the hemC coding region, a possible promoter and three repeated GGATG sequences were identified. This is the first report of a complete DNA sequence for a structural gene specifying an enzyme of the heme biosynthetic pathway in prokaryotes.