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A plasmid, pCKB15, containing a genomic DNA insert from Serratia marcescense KCTC2172 that confer the relation to aconitase was isolated from a shot-gun library constructed in a vector pBluescript KS in Escherichia coli TP2139 on the MacConky medium. A 2.9 kb BamHI fragment, designated acn, was sequenced and found to contain an ORF of 1862 bp encoding a protein of 513 amino acid residues. The predicted amino acid sequence of the Acn protein was similar to that of ACN of E. coli, Pseudomonas sp., Shigella sp., and Bradyrhizobium sp., with similarities of 72, 70, 66, and 57%, respectively. The apparent molecular mass of the protein when expressed in E. coli was approximately 55 kDa. The three cystein residues involved in ligand binding to the [4Fe-4S] centre were conserved in Serratia aconitase. A putative sequence showing good homology with the consensus established for the Fur (the ferric-uptake regulatory protein) and CRP (cAMP receptor protein) binding sites was located in the 5'-untranslated end of Serratia aconitase gene. Using an acn-lacZ protein fusion, it was demonstrated that expression of the S. marcescens ACN was positively regulated by the cAMP-CRP complex and Fur box.