Structure of the processive human Pol δ holoenzyme

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• DNA polymerase delta (Pol δ) and proliferating cell nuclear antigen (PCNA) are crucial for eukaryotic lagging strand DNA replication.
• Processing of Okazaki fragments by Pol δ, PCNA, and flap endonuclease 1 (FEN1) is essential for DNA ligation and genome integrity.

Purpose of the Study:

• To determine the high-resolution cryo-electron microscopy (cryo-EM) structure of the human Pol δ-DNA-PCNA complex.
• To elucidate the structural mechanisms of Pol δ-PCNA interaction and FEN1 recruitment during DNA replication.

Main Methods:

• High-resolution cryo-electron microscopy (cryo-EM) was used to visualize the human Pol δ-DNA-PCNA complex.
• Structures were determined in the absence and presence of flap endonuclease 1 (FEN1).

Main Results:

• The structure shows Pol δ anchored to a PCNA monomer via its C-terminal domain, with the catalytic core positioned on top of PCNA.
• PCNA stabilizes the exiting DNA and recruits FEN1 in a 'toolbelt' fashion to an unoccupied monomer.
• Alternative holoenzyme conformations highlight interactions maintaining PCNA orientation during DNA synthesis.

Conclusions:

• The study provides a detailed structural basis for the function of Pol δ in human genome replication.
• The findings clarify the roles of PCNA and FEN1 in coordinating lagging strand synthesis and Okazaki fragment processing.