Assay of mtDNA Polymerase from Human Tissues

Mitochondrial
DNA
(mtDNA) replication is a complex process involving over 20 proteins organized along the inner mitochondrial membrane as a multienzyme complex called the mtDNA replisome, or replication factory (
1
–
3
). Figure 1 illustrates some of the protein components that participate in mitochondrial DNA replication. A principal component of the mtDNA replisome is the mtDNA polymerase γ. This enzyme is found as an αβ heterodimer and as an α monomer associated with at least four other unidentified cellular proteins (
4
). Both α- and β-subunits have been cloned (
5
–
7
). The α-subunit is catalytic and contains both the polymerase and the 3′ to 5′ proofreading exonuclease activities. It is 140,000 Daltons in size.
Fig. 1.
The mitochondrial DNA replisome. The actual geometry and subunit composition of the mtDNA replisome is not yet known. The proteins shown are those that have been shown to participate in mtDNA replication or repair.