The discovery of four distinct glutamate dehydrogenase genes in a strain of Halobacterium salinarum.

In earlier work, two glutamate dehydrogenase (GDH) proteins were purified from a strain of the halophilic archaeon Halobacterium salinarum (NRC-36014). One of these, an NAD+-specific enzyme, was matched to a cloned gene from H. salinarum (GenBank accession number: X63837 S75579) by sequencing peptide fragments. Analysis of enzymatic digests of the NADP+-GDH and database searching have now established that a gene encoding this protein exists in the full genomic sequence of Halobacterium sp. NRC-1 as gdhA1, together with two other distinct gdh genes, gdhA2 and gdhB. From N-terminal sequence, it is clear that the genomic listing incorrectly assigns the start codon for gdhA1 and the corresponding protein is 43 amino acids longer than previously indicated. The three genes could be amplified by PCR either from NRC-1, as expected, or from NRC-36014 (GenBank accession numbers: YA840085-AY840087). A gene encoding the previously purified NAD+-GDH, is absent from the NRC-1 genome but can be successfully amplified from genomic DNA of NRC-36014 (GenBank accession number: AY840088). This establishes that NRC-36014 contains four gdh genes.

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