The proofreading 3'-->5' exonuclease activity of DNA polymerases: a kinetic barrier to translesion DNA synthesis.

Mutation research (2002), Volume 510, Page 45


The 3'-->5' exonuclease activity intrinsic to several DNA polymerases plays a primary role in genetic stability; it acts as a first line of defense in correcting DNA polymerase errors. A mismatched basepair at the primer terminus is the preferred substrate for the exonuclease activity over a correct basepair. The efficiency of the exonuclease as a proofreading activity for mispairs containing a DNA lesion varies, however, being dependent upon both the DNA polymerase/exonuclease and the type of DNA lesion. The exonuclease activities intrinsic to the T4 polymerase (family B) and DNA polymerase gamma (family A) proofread DNA mispairs opposite endogenous DNA lesions, including alkylation, oxidation, and abasic adducts. However, the exonuclease of the Klenow polymerase cannot discriminate between correct and incorrect bases opposite alkylation and oxidative lesions. DNA damage alters the dynamics of the intramolecular partitioning of DNA substrates between the 3'-->5' exonuclease and polymerase activities. Enzymatic idling at lesions occurs when an exonuclease activity efficiently removes the same base that is preferentially incorporated by the DNA polymerase activity. Thus, the exonuclease activity can also act as a kinetic barrier to translesion synthesis (TLS) by preventing the stable incorporation of bases opposite DNA lesions. Understanding the downstream consequences of exonuclease activity at DNA lesions is necessary for elucidating the mechanisms of translesion synthesis and damage-induced cytotoxicity.



Exonuclease Activity, Kinetic Parameters, Nucleotide Analogs / Template Lesions, Other Enzymatic Activities


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Polymerase Reference Property Result Context
Klenow fragment Khare V2002 3-5' Exonuclease (proofreading) Yes
Klenow fragment Khare V2002 5-3' Exonuclease No
Human Pol gamma Khare V2002 3-5' Exonuclease (proofreading) Yes
Human Pol gamma Khare V2002 5-3' Exonuclease No
T4 Khare V2002 3-5' Exonuclease (proofreading) Yes
T4 Khare V2002 5-3' Exonuclease No
T4 Khare V2002 Extension from RNA primer Yes

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