Evidence for Watson-Crick and not Hoogsteen or wobble base pairing in the selection of nucleotides for insertion opposite pyrimidines and a thymine dimer by yeaηst DNA pol η

Hanshin Hwang, John Stephen Taylor

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

We have recently reported that pyrene nucleotide is preferentially inserted opposite an abasic site, the 3′-T of a thymine dimer, and most undamaged bases by yeast DNA polymerase η (pol η). Because pyrene is a nonpolar molecule with no H-bonding ability, the unusually high efficiencies of dPMP insertion are ascribed to its superior base stacking ability, and underscore the importance of base stacking in the selection of nucleotides by pol η. To investigate the role of H-bonding and base pair geometry in the selection of nucleotides by pol η, we determined the insertion efficiencies of the base-modified nucleotides 2,6-diaminopurine, 2-aminopurine, 6-chloropurine, and inosine which would make a different number of H-bonds with the template base depending on base pair geometry. Watson-Crick base pairing appears to play an important role in the selection of nucleotide analogues for insertion opposite C and T as evidenced by the decrease in the relative insertion efficiencies with a decrease in the number of Watson-Crick H-bonds and an increase in the number of donor-donor and acceptor-acceptor interactions. The selectivity of nucleotide insertion is greater opposite the 5′-T than the 3′-T of the thymine dimer, in accord with previous work suggesting that the 5′-T is held more rigidly than the 3′-T. Furthermore, insertion of A opposite both Ts of the dimer appears to be mediated by Watson-Crick base pairing and not by Hoogsteen base pairing based on the almost identical insertion efficiencies of A and 7-deaza-A, the latter of which lacks H-bonding capability at N7. The relative efficiencies for insertion of nucleotides that can form Watson-Crick base pairs parallel those for the Klenow fragment, whereas the Klenow fragment more strongly discriminates against mismatches, in accord with its greater shape selectivity. These results underscore the importance of H-bonding and Watson-Crick base pair geometry in the selection of nucleotides by both pol η and the Klenow fragment, and the lesser role of shape selection in insertion by pol η due to its more open and less constrained active site.

Original languageEnglish
Pages (from-to)4850-4860
Number of pages11
JournalBiochemistry
Volume44
Issue number12
DOIs
StatePublished - Mar 29 2005

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