ISOLATION AND CHARACTERIZATION OF A CDNA THAT ENCODES MAIZE GLUTAMATE-DEHYDROGENASE

A full-length cDNA clone, pMGDH1, encoding maize NADH-glutamate dehydr ogenase (NADH-GDH) was isolated from a maize root cDNA library. The id entity of the cDNA was established by the coincidence of the structure of the purified protein with that inferred from the nucleotide sequen ce of the cDNA. pMGDH1 had a cDNA insert of 1,638 bp and the open read ing frame encoded 411 amino acid residues. The deduced amino acid sequ ence was similar to putative partial sequences of GDHs from higher pla nts and to the sequences of GDHs from organisms as diverse as mammals and bacteria. The NH2-terminal sequence deduced from the open reading frame had a typical structure that is associated with the import of pr oteins into the mitochondrial matrix. The cDNA hybridized to an RNA of about 1.6 kb. This transcript was more abundant in roots than in leav es and was localized in the bundle sheath cells in leaf tissues. Analy sis of genomic DNA by Southern hybridization suggested the existence o f gene(s) for another NADH-GDH subunit(s).