Sequence and expression of an isocitrate dehydrogenase-encoding gene from a polycyclic aromatic hydrocarbon oxidizer,...

An 18.5-kb DNA fragment was cloned from Sphingomonas yanoikuyae (Sy) B1 (previously Beijerinckia B1). Analysis of a 4.3-kb sequence revealed an isocitrate dehydrogenase (Idh)-encoding gene (idhA), an unidentified open reading frame (ORF) and a partial glucosamine synthetase-encoding ORF (glmS). As in a number of bacteria, Tn7 insertion was found specifically at a site past the stop codon of glmS. The predicted 406-amino-acid sequence of IdhA shows, for the first time, an extensive sequence identity (66%) with an eukaryotic NADP+-specific Idh. The idhA gene was expressed in Escherichia coli. Identical restriction fragments carrying idhA were found in B1, Sy IFO15102 and Sy Q1 (formerly S. paucimobilis Q1), indicating a well-conserved idh gene.