DNA Polymerase β from Brain Neurons Is a Repair Enzyme

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Abstract
DNA polymerase β was isolated from rat cortex neurons and characterised. Its properties were strikingly similar to those of other mammalian β-polymerases. In adult rats, this was the major DNA polymerase occurring in neuronal nuclei, which contained no α-polymerase, 99.2%β-polymerase and only 0.8%γ-polymerase. Isolated neuronal nuclei of this developmental stage were shown to perform ultraviolet-induced repair DNA synthesis in vitro. Since β-polymerase was virtually the exclusive DNA polymerase in these nuclei it was concluded that the β enzyme was responsible for the observed DNA repair. This was further substantiated by demonstrating a virtually complete suppression of DNA repair in irradiated nuclei by 2′,3′-dideoxyribosylthymine 5′-triphosphate (d2TTP), a potent β-polymerase inhibitor. However, the presence of minute amounts of γ-polymerase in neuronal nuclei and its susceptibility to d2TTP did not allow one to rule out an ancillary role of DNA polymerase γ in DNA repair. In view of the similarity of the neuronal DNA polymerase β with all other mammalian β-polymerases it may be speculated that the ability to perform repair DNA synthesis is not unique to the neuronal enzyme but is a general function of all β-polymerases.