Unorthodox PCNA Binding by Chromatin Assembly Factor 1

Area of Science:

• Molecular Biology
• Epigenetics
• DNA Replication

Background:

• The DNA replication fork involves numerous enzymes for DNA synthesis, epigenetic modification, and chromatin packaging.
• Proliferating cell nuclear antigen (PCNA) is a key scaffold protein that binds many of these enzymes.
• Understanding how PCNA-binding proteins interact without interference is crucial for deciphering DNA replication regulation.

Purpose of the Study:

• To investigate the binding mechanism between Chromatin Assembly Factor 1 (CAF-1) and PCNA.
• To elucidate how CAF-1's interaction with PCNA contributes to DNA replication and chromatin assembly.

Main Methods:

• Biochemical assays to study protein-protein interactions.
• Site-directed mutagenesis to investigate the role of specific amino acid residues.
• Analysis of evolutionary conservation of protein domains.

Main Results:

• CAF-1 binds PCNA through a previously uncharacterized cation-pi (π) interaction.
• A conserved arginine residue in CAF-1, absent in other PCNA-binding proteins, mediates this interaction by binding to PCNA's hydrophobic pocket.
• Mutating this arginine disrupts CAF-1's ability to bind PCNA and assemble chromatin.
• The CAF-1 p150 subunit features a long, DNA-binding alpha-helix terminating in a PCNA-interacting peptide (PIP), conserved across species.

Conclusions:

• CAF-1 utilizes a unique binding mode with PCNA, distinct from canonical PIPs, involving a cation-pi interaction.
• This novel interaction mechanism is essential for CAF-1's function in chromatin assembly during DNA replication.
• The conserved structure of CAF-1, with its long DNA-binding helix and C-terminal PIP, may coordinate DNA binding and PCNA interaction.