SELECTION, EXPRESSION, AND NUCLEOTIDE SEQUENCING OF THE GLUTAMATE-DEHYDROGENASE GENE OF PEPTOSTREPTOCOCCUS-ASACCHAROLYTICUS

The gene for the catabolic NAD-linked glutamate dehydrogenase of Peptostreptococcus asaccharolyticus was cloned by selection in Escherichia coli for complementation of a biosynthetic defect. Cloned fragments containing the gene and the P. asaccharolyticus transcription and translation signals are very highly expressed in E. coli. The nucleotide sequence of the cloned gene was determined. It codes for a polypeptide of 421 amino acids, the sequence of which is similar to those of the NADP-accepting glutamate dehydrogenases. The sequence similarity of this protein to the mammalian glutamate dehydrogenases, which accept both NADP and NAD, is greater than its similarity to the bacterial NADP-specific dehydrogenases, suggesting that this NAD-specific bacterial glutamate dehydrogenase and the NADP-specific bacterial dehydrogenases diverged separately from the line leading to the dual-specificity mammalian glutamate dehydrogenases.