Abstract
The (5′S)‐8,5′‐cyclo‐2′‐deoxyguanosine (S‐cdG) DNA adduct is produced from reactions of DNA with hydroxyl radicals generated from ionizing radiation or endogenous oxidative metabolisms. An elevated level of S‐cdG has been detected in Xeroderma pigmentosum, Cockayne syndrome and breast cancer patients, and in aged mice. S‐dG blocks DNA replications in vitro and in human cells, and is repaired by synergetic actions of nucleotide excision repair and translesion DNA synthesis. S‐cdG induces G to A transition in E coli and in human cells, and causes S‐cdG:T mispair in vitro with several translesion DNA polymerases. However, the molecular mechanisms of translesion bypass of S‐cdG remain elusive. We examined kinetic and structural mechanisms of S‐cdG bypass using model DNA polymerases, Sulfolobus Solfataricus DNA Polymerase I (Dpo1) and IV (Dpo4). Both Dpo1 and Dpo4 can moderately bypass S‐cdG with much lower catalytic efficiencies compared to efficiencies with an undamaged template. Dpo1 and Dpo4 bypassed the lesion in a largely error‐free fashion. Pre‐steady‐state kinetics analyses revealed that the lowered catalytic efficiency of Dpo4 in the presence of template S‐cdG derived from a lower DNA binding affinity and an attenuated formation of the productive enzyme‐DNA‐nucleotide complex. To provide structural insights, we solved two X‐ray crystal structures containing Dpo4, S‐cdG‐containing DNA duplex, and the correct dCTP or incorrect dTTP. Together, our study provided mechanistic insights for the translesion bypass across a highly mutagenic cyclopurine lesion.
Published Version
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