A unique error signature for human DNA polymerase nu

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Human DNA polymerase nu (pol nu) is an A family polymerase with unknown biological functions.
• It is implicated in DNA repair and translesion DNA synthesis (TLS).
• Pol nu lacks proofreading and shows poor discrimination against misinsertion, suggesting low fidelity.

Purpose of the Study:

• To comprehensively examine human pol nu DNA synthesis fidelity.
• To investigate pol nu error rates for base substitutions, insertions, and deletions.
• To use fidelity data as a clue to pol nu's function.

Main Methods:

• Assessed pol nu error rates using the lacZ alpha-complementation assay in M13mp2 DNA.
• Quantified all 12 single base-base mismatches, insertion, and deletion errors.
• Analyzed sequence contexts of prevalent errors.

Main Results:

• Pol nu showed average single-base insertion and deletion error rates of 7 x 10(-5) and 17 x 10(-5), respectively.
• The average single-base substitution error rate was 3.5 x 10(-3), comparable to Y family TLS polymerases.
• A majority of errors involved dTMP misincorporation opposite template G, especially after C-G or G-C pairs, reaching >10% in some contexts.

Conclusions:

• Human pol nu possesses low base substitution fidelity, similar to Y family TLS polymerases.
• Its unique error signature, particularly misincorporation of dTMP opposite template G, may be linked to its function.
• Structural differences in pol nu's O-helix might explain its distinct error profile.