Coupling the mitochondrial transcription machinery to human disease.

Mitochondria are the central processing units for cellular energy metabolism and, in addition to carrying out oxidative phosphorylation, regulate important processes such as apoptosis and calcium homeostasis. Because mitochondria possess a genome that is central to their multiple functions, an understanding of the mechanism of mitochondrial gene expression is required to decipher the many ways mitochondrial dysfunction contributes to human disease. Towards this end, two human transcription factors that are related to rRNA methyltransferases have recently been characterized, providing new insight into the mechanism of mitochondrial transcription and a novel link to maternally inherited deafness. Furthermore, studies in the Saccharomyces cerevisiae model system have revealed a functional coupling of transcription and translation at the inner mitochondrial membrane, where assembly of the oxidative phosphorylation system commences. Defects in an analogous coupling mechanism in humans might underlie the cytochrome oxidase deficiency that causes a form of Leigh Syndrome.