Molecular cloning of an inulin fructotransferase (depolymerizing) gene from Arthrobacter sp. H65-7 and its expression in Escherichia coli.

The gene encoding an extracellular inulin fructotransferase (depolymerizing) (inulase II) (EC 2.4.1.93), designated ift gene, was cloned from the genomic DNA of Arthrobacter sp. H65-7, and expressed in Escherichia coli for the first time. Sequence analysis showed a single open reading frame consisting of 1314 base pairs that encoded a signal peptide of 32 amino acids and a mature protein of 405 amino acids. The primary structure showed a homology of 49.8% with that of the inulin fructotransferase (DFA I-producing) (EC 2.4.1.200) from Arthrobacter globiformis S14-3. E. coli cells carrying the ift gene produced the active enzyme under control of the lac promoter. The expression of the ift gene was improved by a plasmid, pIFT-B, in which the ift gene was immediately downstream from the lac promoter. An E. coli transformant carrying pIFT-B expressed twice as much activity of inulase II as that of the original strain, Arthrobacter sp. H65-7. Most of the enzyme activity existed within the cells.