Coordination between human DNA polymerase ß and apurinic/apyrimidinic endonuclease 1 in the course of DNA repair.

Coordination of enzymatic activities in the course of base excision repair (BER) is essential to ensure complete repair of damaged bases. Two major mechanisms underlying the coordination of BER are known today: the "passing the baton" model and a model of preassembled stable multiprotein repair complexes called "repairosomes." In this work, we aimed to elucidate the coordination between human apurinic/apyrimidinic (AP) endonuclease APE1 and DNA polymerase Polß in BER through studying an impact of APE1 on Polß-catalyzed nucleotide incorporation into different model substrates that mimic different single-strand break (SSB) intermediates arising along the BER pathway. It was found that APE1's impact on separate stages of Polß's catalysis depends on the nature of a DNA substrate. In this complex, APE1 removed 3' blocking groups and corrected Polß-catalyzed DNA synthesis in a coordinated manner. Our findings support the hypothesis that Polß not only can displace APE1 from damaged DNA within the "passing the baton" model but also performs the gap-filling reaction in the ternary complex with APE1 according to the "repairosome" model. Taken together, our results provide new insights into coordination between APE1 and Polß during the BER process.

The Impact of Human DNA Glycosylases on the Activity of DNA Polymerase ß toward Various Base Excision Repair Intermediates.

Base excision repair (BER) is one of the important systems for the maintenance of genome stability via repair of DNA lesions. BER is a multistep process involving a number of enzymes, including damage-specific DNA glycosylases, apurinic/apyrimidinic (AP) endonuclease 1, DNA polymerase ß, and DNA ligase. Coordination of BER is implemented by multiple protein-protein interactions between BER participants. Nonetheless, mechanisms of these interactions and their roles in the BER coordination are poorly understood. Here, we report a study on Polß's nucleotidyl transferase activity toward different DNA substrates (that mimic DNA intermediates arising during BER) in the presence of various DNA glycosylases (AAG, OGG1, NTHL1, MBD4, UNG, or SMUG1) using rapid-quench-flow and stopped-flow fluorescence approaches. It was shown that Polß efficiently adds a single nucleotide into different types of single-strand breaks either with or without a 5'-dRP-mimicking group. The obtained data indicate that DNA glycosylases AAG, OGG1, NTHL1, MBD4, UNG, and SMUG1, but not NEIL1, enhance Polß's activity toward the model DNA intermediates.