A non-catalytic role for RFC in PCNA-mediated processive DNA synthesis

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Proliferating cell nuclear antigen (PCNA) is a ring-shaped sliding clamp crucial for DNA replication and repair.
• Replication factor C (RFC) is an ATPase that loads PCNA onto DNA.

Purpose of the Study:

• To investigate the dynamic interaction between PCNA and RFC on DNA using single-molecule imaging.
• To elucidate the functional significance of the RFC-PCNA interaction beyond canonical clamp loading.

Main Methods:

• Single-molecule imaging to visualize PCNA-RFC dynamics on DNA.
• Biochemical assays to assess the stability of PCNA-polymerase complexes.
• In vivo studies using mutant RFC proteins to evaluate genotoxic stress sensitivity.

Main Results:

• RFC unexpectedly remains associated with PCNA after loading, forming a clamp-loader/clamp (CLC) complex.
• This CLC complex is essential for processive DNA synthesis by polymerase ẟ (Polẟ) due to inherent instability of the PCNA-Polẟ assembly.
• The architectural role of RFC depends on its BRCT domain, and mutations impairing DNA binding lead to genotoxic stress sensitivity.
• Flap endonuclease I (FEN1) also stabilizes the PCNA-Polẟ interaction, supporting robust DNA synthesis.

Conclusions:

• PCNA-binding proteins, including RFC, possess non-catalytic functions vital for DNA replication and genome maintenance.
• RFC's sustained association with PCNA plays a critical architectural role in stabilizing DNA polymerase activity.
• Understanding these non-canonical functions is key to comprehending DNA replication fidelity and genome stability.