The mammalian mitochondrion. The mitochondrion is the site of ATP generation via the tricarboxylic acid (TCA) cycle and the electron-transport chain, and the mitochondrial genome (mtDNA) exists in multiple copies per mitochondrion. The majority of mitochondrially localized proteins, including the basal transcription machinery (Tfam, Tfb2m and Polmrt), are encoded in the nucleus, where their expression is controlled by nuclear transcription factors (such as the estrogen receptor (ER) and NRF-1). Their mRNAs are then translated in the cytoplasm and the proteins imported into mitochondria.
Leigh-Brown et al. Genome Biology 2010 11:215 doi:10.1186/gb-2010-11-7-215