Mitochondrial Genome Rearrangement Leads to Extension and Relocation of the Cytochrome C Oxidase Subunit I Gene in Sorghum

The mitochondrial gene (COXI) encoding cytochrome c oxidase subunit I (COI) was isolated from two cytoplasmic genotypes of sorghum that synthesize different COI polypeptides. The Milo COI (Mr approximately 38,000) is encoded by a 530 codon structural gene sharing 98% homology with the corresponding maize gene. A variant COI observed in 9E cytoplasm (Mr approximately 42,000) is encoded by a 631 codon structural gene that diverges completely from the Milo COXI gene both 100 bp 5' to the presumed initiator methionine and within the 3' coding sequence. The 3' divergence results in a 101 C-terminal extension of the 9E COI that is not homologous to any known mitochondrial polypeptide. The novel 9E COXI, apparently arising from at least two rearrangements, affects transcription and gene product.