DNA Polymerase α has pyrimidine dimer translesion activity that is suppressed during normal replication

Area of Science:

• Molecular Biology
• DNA Replication
• DNA Repair

Background:

• UV radiation damages DNA, forming pyrimidine dimers that stall replication forks.
• DNA damage tolerance (DDT) pathways, including Translesion Synthesis (TLS), allow replication to bypass lesions.
• Specialized TLS polymerases handle lesion bypass during DNA replication.

Purpose of the Study:

• To investigate the potential Translesion Synthesis (TLS) activity of DNA Polymerase alpha (Pol α) on cyclobutane pyrimidine dimer (CPD) lesions.
• To characterize the biochemical and genetic basis of Pol α's interaction with CPDs.
• To determine how other replication fork proteins affect Pol α's TLS activity.

Main Methods:

• Biochemical assays to assess Pol α's polymerase activity on CPD-containing DNA.
• Single-molecule Fluorescence Resonance Energy Transfer (FRET) to study DNA binding dynamics.
• Yeast genetics to evaluate the in vivo function of Pol α in UV sensitivity.

Main Results:

• DNA Polymerase alpha (Pol α) exhibits robust in vitro TLS activity on CPD lesions without misincorporation.
• Pol α's DNA binding cleft accommodates CPD lesions, suggesting a mechanism for bypass.
• Overexpression of Pol α did not rescue UV sensitivity in a TLS-deficient strain.
• Replication protein A (RPA), Pol ε, and Pol δ inhibit Pol α's CPD TLS activity.

Conclusions:

• DNA Polymerase alpha (Pol α) possesses intrinsic TLS activity capable of bypassing CPD lesions.
• The TLS activity of Pol α is actively suppressed by other replication fork components (RPA, Pol ε, Pol δ) during normal replication.
• This suppression mechanism likely prevents Pol α from engaging in TLS under physiological conditions, ensuring fidelity.