Human PrimPol is a highly error-prone polymerase regulated by single-stranded DNA binding proteins.

Area of Science:

• Molecular Biology
• DNA Replication and Repair
• Enzymology

Background:

• PrimPol is a novel polymerase crucial for eukaryotic DNA damage tolerance.
• It participates in re-priming and translesion synthesis to bypass DNA lesions.
• Understanding PrimPol's regulation is key to its role in genome stability.

Purpose of the Study:

• To investigate the regulatory mechanisms of human PrimPol enzymatic activities.
• To determine PrimPol's interaction partners and their effect on its function.
• To characterize PrimPol's replication fidelity and error specificity.

Main Methods:

• In vivo interaction studies to identify binding partners.
• Nuclear Magnetic Resonance (NMR) spectroscopy to map protein-protein interaction domains.
• Forward mutation assays to assess replication fidelity and error rates.

Main Results:

• PrimPol does not interact with PCNA, unlike other translesion synthesis polymerases.
• PrimPol interacts with RPA and mtSSB; NMR reveals binding to RPA70 N-terminal domain.
• Single-strand binding proteins (SSBs) significantly inhibit PrimPol's primase and polymerase activities.
• PrimPol is a mutagenic polymerase with a high bias for insertion-deletion errors.
• SSBs restrict PrimPol's activity at stalled replication forks, reducing its mutagenic potential.

Conclusions:

• Human PrimPol activity is uniquely regulated by SSBs, contrasting with other TLS polymerases.
• SSB-mediated limitation of PrimPol function serves as a safeguard against excessive mutagenesis.
• This regulation mechanism is critical for maintaining genome integrity during DNA replication stress.