Human PIF1 clears secondary DNA structures by coupled DNA unwinding and rewinding activities.

Human PIF1 primarily functions as a DNA translocase that couples unwinding with rapid rewinding to clear secondary DNA structures, with only weak net unwinding observed.

• Why it matters: Understanding the biochemical activity of human PIF1 is crucial because PIF1 helicases promote genome stability during DNA replication and repair, yet its precise mechanism remains unclear.
• What they did: Researchers compared full-length human PIF1 and yeast Pif1 using bulk assays, single-molecule magnetic tweezers, mutagenesis, and structural modeling, revealing functional differences and activity modes.
• The result: Findings show that human PIF1 efficiently remodels G-quadruplex DNA into fully base-paired dsDNA without extensive ssDNA formation, suggesting it acts mainly as a DNA translocase coupling unwinding with rewinding.