Identity of DNA Polymerase γ from Synaptosomal Mitochondria and Rat‐Brain Nuclei

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Abstract
DNA polymerase γ and mitochondrial DNA polymerase were isolated from brain nuclei and synaptosomes respectively. The presence of a single DNA polymerase in synaptosomal mitochondria was established by chromatography on DEAE‐cellulose, phosphocellulose and DNA‐cellulose, as well as by sedimentation analysis and isoelectric focusing. A great similarity between the purified nuclear DNA polymerase γ and the mitochondrial enzyme was found by the following criteria: chromatographic behaviour in three column systems; essentially complete inhibition by N‐ethylmaleimide (2 mM); optimal requirements for Mn2+ (0.1 mM), Mg2+ (5 mM) and pH (8.0); template preferences, poly(A) · (dT)20–25 > activated DNA > poly(dA) · (dT)12–18; lack of activity on single‐stranded polynucleotides and (dT)12‐primed mRNA; molecular weight (180 000), sedimentation (9.2 S) and isoelectric point (pI5.4). We therefore conclude that brain nuclear DNA polymerase 7 and synaptosomal mitochondrial DNA polymerase are closely related and may even be identical.