Genomic cloning and characterization of mitochondrial elongation factor Tu (EF-Tu) gene ( tufM) from maize ( Zea mays L.)

We have cloned and characterized a mitochondrial elongation factor Tu (EF-Tu) gene ( tufM) in maize ( Zea mays L.). This maize tufM gene encoded a polypeptide of 452 amino acid residues, consisting of a putative transit peptide of 55 residues and a mature EF-Tu of 397 residues. The coding region was composed of 12 exons and 11 introns that ranged from 76 to 1673 bp in length. The deduced amino acid sequence showed 85.9% and 61.2% identity with Arabidopsis mitochondrial EF-Tu and Arabidopsis chloroplast EF-Tu sequence respectively. The transcription initiation site was determined to be 165 bp upstream of the AUG initiation codon by primer extension analysis. Southern blot analysis revealed that the cloned EF-Tu gene was encoded by the members of small gene family in maize. Although this gene does not resemble the Arabidopsis nuclear tufA gene, which encodes the plastid EF-Tu, and does not contain sequence elements found in all cyanobacterial and plastid tufA genes, the predicted amino acid sequence includes an N-terminal extension that resembles a mitochondrial targeting sequence, and shares three unique sequence elements with mitochondrial EF-Tu's from Arabidopsis thaliana, Saccharomyces cerevisiae, and Homo sapiens. Therefore, we concluded that this gene encodes the maize mitochondrial EF-Tu.