Human Mitochondrial DNA Polymerase Metal Dependent UV Lesion Bypassing Ability.

Human mitochondrial DNA contains more UV-induced lesions than the nuclear DNA due to lack of mechanism to remove bulky photoproducts. Human DNA polymerase gamma (Pol γ) is the sole DNA replicase in mitochondria, which contains a polymerase () and an exonuclease () active site. Previous studies showed that Pol γ only displays UV lesion bypassing when its exonuclease activity is obliterated. To investigate the reaction environment on Pol γ translesion activity, we tested Pol γ DNA activity in the presence of different metal ions. While Pol γ is unable to replicate through UV lesions on DNA templates in the presence of Mg, it exhibits robust translesion DNA synthesis (TLS) on cyclobutane pyrimidine dimer (CPD)-containing template when Mg was mixed with or completely replaced by Mn. Under these conditions, the efficiency of Pol γ's TLS opposite CPD is near to that on a non-damaged template and is 800-fold higher than that of exonuclease-deficient Pol γ. Interestingly, Pol γ exhibits higher exonuclease activity in the presence of Mn than with Mg, suggesting Mn-stimulated Pol γ TLS is not via suppressing its exonuclease activity. We suggest that Mn ion expands Pol γ's active site relative to Mg so that a UV lesion can be accommodated and blocks the communication between and active sites to execute translesion DNA synthesis.