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The 3'-5' proofreading exonuclease of archaeal family-B DNA polymerase hinders the copying of template strand deaminated bases

Lookup NU author(s): Henry Russell, Dr Tom Richardson, Kieran Emptage, Professor Bernard Connolly

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Abstract

Archaeal family B polymerases bind tightly to the deaminated bases uracil and hypoxanthine in single-stranded DNA, stalling replication on encountering these pro-mutagenic deoxynucleosides four steps ahead of the primer-template junction. When uracil is specifically bound, the polymerase-DNA complex exists in the editing rather than the polymerization conformation, despite the duplex region of the primer-template being perfectly base-paired. In this article, the interplay between the 3'-5' proofreading exonuclease activity and binding of uracil/hypoxanthine is addressed, using the family-B DNA polymerase from Pyrococcus furiosus. When uracil/hypoxanthine is bound four bases ahead of the primer-template junction (+4 position), both the polymerase and the exonuclease are inhibited, profoundly for the polymerase activity. However, if the polymerase approaches closer to the deaminated bases, locating it at +3, +2, +1 or even 0 (paired with the extreme 3' base in the primer), the exonuclease activity is strongly stimulated. In these situations, the exonuclease activity is actually stronger than that seen with mismatched primer-templates, even though the deaminated base-containing primer-templates are correctly base-paired. The resulting exonucleolytic degradation of the primer serves to move the uracil/hypoxanthine away from the primer-template junction, restoring the stalling position to +4. Thus the 3'-5' proofreading exonuclease contributes to the inability of the polymerase to replicate beyond deaminated bases.


Publication metadata

Author(s): Russell HJ, Richardson TT, Emptage K, Connolly BA

Publication type: Article

Publication status: Published

Journal: Nucleic Acids Research

Year: 2009

Volume: 37

Issue: 22

Pages: 7603-7611

Date deposited: 06/04/2010

ISSN (print): 0305-1048

ISSN (electronic): 1362-4962

Publisher: Oxford University Press

URL: http://dx.doi.org/10.1093/nar/gkp800

DOI: 10.1093/nar/gkp800


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