Proliferating cell nuclear antigen (PCNA) is a multifunctional protein present in the nuclei of eukaryotic cells that plays an important role as a component of the DNA replication machinery, as well as DNA repair systems. PCNA was recently proposed as a potential non-oncogenic target for anti-cancer therapy. In this study, using the Systematic Evolution of Ligands by EXponential enrichment (SELEX) method, we developed a short DNA aptamer that binds human PCNA. In the presence of PCNA, the anti-PCNA aptamer inhibited the activity of human DNA polymerase and at nM concentrations. Moreover, PCNA protected the anti-PCNA aptamer against the exonucleolytic activity of these DNA polymerases. Investigation of the mechanism of anti-PCNA aptamer-dependent inhibition of DNA replication revealed that the aptamer did not block formation, but was a component of PCNA/DNA polymerase or complexes. Additionally, the anti-PCNA aptamer competed with the primer-template DNA for binding to the PCNA/DNA polymerase or complex. Based on the observations, a model of anti-PCNA aptamer/PCNA complex-dependent inhibition of DNA replication was proposed.
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