Human DNA polymerase N (POLN) is a low fidelity enzyme capable of error-free bypass of 5S-thymine glycol.


Human DNA polymerase N (POLN or pol nu) is the most recently discovered nuclear DNA polymerase in the human genome. It is an A-family DNA polymerase related to Escherichia coli pol I, human POLQ, and Drosophila Mus308. We report the first purification of the recombinant enzyme and examination of its biochemical properties, as a step toward understanding the functions of POLN. Unusual for an A-family DNA polymerase, POLN is a low fidelity enzyme incorporating T opposite template G with a frequency of 0.45 and G opposite template T with a frequency of 0.021. The frequency of misincorporation of T opposite template G is higher than any other known DNA polymerase. POLN has a processivity of DNA synthesis (1-100 nucleotides) similar to the exonuclease-deficient Klenow fragment of E. coli pol I, is inhibited by dideoxynucleotides, and resistant to aphidicolin. The strand displacement activity of POLN was higher than exonuclease-deficient Klenow fragment. Furthermore, POLN can perform translesion synthesis past thymine glycol, a common endogenous and radiation-induced product of reactive oxygen species damage to DNA. Thymine glycol blocks DNA synthesis by most DNA polymerases, but POLN was particularly adept at efficient and accurate translesion synthesis past a 5S-thymine glycol.



Historical Protein Properties (MW, pI, ...), Exonuclease Activity, Nucleotide Analogs / Template Lesions, Structure and Structure/Function, Nucleotide Incorporation


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Polymerase Reference Property Result Context
Human Pol nu Takata K2006 Molecular Weight 100kD
Human Pol nu Takata K2006 3-5' Exonuclease (proofreading) No
Human Pol nu Takata K2006 Template lesions Stalls Reaction: Nucleotide incorporation; DNA lesion: Apurinic/Apyrimidinic (AP) site
Human Pol nu Takata K2006 Template lesions Stalls Reaction: Nucleotide incorporation; DNA lesion: TT Cyclobutane Pyrimidine Dimer
Human Pol nu Takata K2006 Amino Acids Contacting NTP D623A
Human Pol nu Takata K2006 Processivity 150bp
Human Pol nu Takata K2006 Nick Extension Yes, via strand displacement
Human Pol nu Takata K2006 Strand Displacement Yes

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