Molecular analysis of the Corynebacterium glutamicum gdh gene encoding glutamate dehydrogenase

Summary The Corynebacterium glutamicum gdh gene encoding NADP‐dependent glutamate dehydrogenase (GDH) has been isolated by complementation of the Escherichia coli gdh mutant PA340. The gdh gene was subcloned into the E. coli/C. glutamicum shuttle vector pEK0 and introduced into C. glutamicum. Recombinant strains showed approximately eightfold higher specific GDH activity (15U mg protein ‐1 ) relative to the wild type (1.8U mg protein ‐1 ). Physiological studies with wild‐type and recombinant C. glutamicum strains revealed no indication of significant regulation of gdh expression. The DNA sequence of 2082 bp, including the gdh gene, 5′‐, and 3′‐flanking regions, was determined. The structural gene consists of 1344 bp and codes for a polypeptide of 448 amino acid residues ( M r 49152) showing up to 53.6% identity with reported amino acid sequences of glutamate dehydrogenases from other organisms. Northern blot hybridization revealed a 1.65 kb mRNA transcript, indicating that the gdh gene of C. glutamicum is monocistronic. Transcription occurred from a G residue located 284bp upstream of the AUG considered to be the translational initiation codon.