Resolving a fidelity paradox: why Escherichia coli DNA polymerase II makes more base substitution errors in AT- compared with GC-rich DNA.
The activity of DNA polymerase-associated proofreading 3'-exonucleases is generally enhanced in less stable DNA regions leading to a reduction in base substitution error frequencies in AT- versus GC-rich sequences. Unexpectedly, however, the opposite result was found for Escherichia coli DNA polymerase II (pol II). Nucleotide misincorporation frequencies for pol II were found to be 3-5-fold higher in AT- compared with GC-rich DNA, both in the presence and absence of polymerase processivity subunits, beta dimer and gamma complex. In contrast, E. coli pol III holoenzyme, behaving "as expected," exhibited 3-5-fold lower misincorporation frequencies in AT-rich DNA. A reduction in fidelity in AT-rich regions occurred for pol II despite having an associated 3'-exonuclease proofreading activity that preferentially degrades AT-rich compared with GC-rich DNA primer-template in the absence of DNA synthesis. Concomitant with a reduction in fidelity, pol II polymerization efficiencies were 2-6-fold higher in AT-rich DNA, depending on sequence context. Pol II paradoxical fidelity behavior can be accounted for by the enzyme's preference for forward polymerization in AT-rich sequences. The more efficient polymerization suppresses proofreading thereby causing a significant increase in base substitution error rates in AT-rich regions.
Wang
Zhijie
Z
Department of Biological Sciences, Hedco Molecular Biology Laboratories, University of Southern California, Los Angeles, California 90089-1340, USA.
Lazarov
Eli
E
O'Donnell
Mike
M
Goodman
Myron F
MF
D001483:Base Sequence; D004257:DNA Polymerase II / Q000378:metabolism*; D017931:DNA Primers; D004261:DNA Replication; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D009154:Mutation; D013698:Templates, Genetic
D017931:DNA Primers; D004257:DNA Polymerase II