The ATPase subunit 6 gene of tobacco mitochondria contains an unusual sequence

Summary We have isolated and characterized the F₀-ATPase subunit 6 gene (atp6) from tobacco mitochondria. The tobacco sequence exists as a single copy, is transcribed and contains an open reading frame (ORF) capable of encoding a peptide of 395 amino acids. The first 130 amino acids of the tobacco putative polypeptide show limited homology with the N terminus predicted for the maize ATPase subunit 6. Although poorly conserved at the sequence level, the tobacco and maize amino termini are hydrophilic and have a high percentage of charged amino acids. This portion of the predicted peptide may represent a presequence that is common to the ATPase subunit 6 of plants. Significant homology between tobacco and maize begins with amino acid 131, in a region that is highly conserved among fungal ATPase 6 subunits. In the remainder of the predicted protein, tobacco and maize share approximately 81% homology. A 41 by sequence and a 175 by conserved region found upstream from the tobacco atp6 coding region are homologous with sequence elements found in the 5 flanking regions of other plant mitochondrial genes and may be important for regulation and expression of the atp6 gene.