Structural insight into translesion synthesis by DNA Pol II

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology
• Genetics

Background:

• B-family polymerases, including E. coli DNA Pol II and eukaryotic Rev3, are crucial for DNA repair.
• High-fidelity replicative polymerases can be ineffective at replicating DNA past damaged or mismatched sites.
• Translesion synthesis (TLS) is a mechanism employed by specialized polymerases to bypass DNA lesions.

Purpose of the Study:

• To elucidate the biochemical and structural properties of E. coli DNA Pol II that enable translesion synthesis.
• To understand the mechanisms by which DNA Pol II bypasses DNA lesions, including template skipping.
• To investigate how DNA Pol II balances efficient replication of undamaged DNA with TLS capability.

Main Methods:

• Biochemical assays to characterize DNA Pol II activity.
• Structural studies to determine the three-dimensional structure of DNA Pol II.
• Analysis of DNA substrate partitioning between active and exonuclease sites.

Main Results:

• DNA Pol II can extend primers past lesions directly or via template skipping, accommodating looped-out template nucleotides in small cavities.
• The ability to accommodate multiple looping-out alternatives complicates the mutation spectra of bypass synthesis.
• Altered partitioning of DNA substrate between the active site and proofreading exonuclease site enhances TLS.
• Subtle amino acid changes remote from the active site allow DNA Pol II to efficiently replicate normal DNA while also performing TLS.

Conclusions:

• DNA Pol II possesses unique structural and biochemical properties that facilitate efficient translesion synthesis.
• Template skipping and altered substrate partitioning are key mechanisms enabling DNA Pol II to bypass DNA damage.
• DNA Pol II represents a specialized B-family polymerase capable of high-fidelity replication and damage tolerance.