Structural analysis of a eukaryotic sliding DNA clamp-clamp loader complex.

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Sliding clamps, such as proliferating cell nuclear antigen (PCNA), encircle DNA to enhance DNA polymerase processivity.
• The clamp loader complex, replication factor-C (RFC), is essential for loading PCNA onto DNA.
• Understanding the structural basis of RFC-PCNA interaction is crucial for elucidating DNA replication mechanisms.

Purpose of the Study:

• To determine the crystal structure of the Saccharomyces cerevisiae RFC-PCNA complex.
• To elucidate the mechanism by which RFC loads PCNA onto primed DNA.

Main Methods:

• X-ray crystallography was used to determine the structure of the RFC-PCNA complex bound to an ATP analogue (ATP-gammaS).
• A model of primed DNA was placed within the PCNA ring to visualize the interaction interface.

Main Results:

• The crystal structure revealed a spiral arrangement of RFC's ATPase domains above the PCNA ring.
• This spiral structure exhibits a striking correspondence with the grooves of the DNA double helix.
• A screw-cap-like model for RFC binding to primed DNA was proposed.

Conclusions:

• The RFC spiral structure facilitates a lock-and-key mechanism for engaging primer-template junctions.
• This interaction triggers ATP hydrolysis and the subsequent release of PCNA onto DNA.
• The findings provide a structural explanation for the loading of sliding clamps in DNA replication.