Nucleic Acids Research, 2001, Vol. 29, No. 20 4206-4214
© 2001 Oxford University Press
Arg660Ser mutation in Thermus aquaticus DNA polymerase I suppresses T
C transitions: implication of wobble base pair formation at the nucleotide incorporation step
Division of Surgical Oncology, Department of Surgery and 1Laboratory of Cancer Cell Biology, Research Institute for Disease Mechanism and Control, Nagoya University Graduate School of Medicine, Tsurmai-cho, Showa-ku, Nagoya 466-8550, Japan, 2Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan, 3Nagoya University School of Health Science, Nagoya 461-8673, Japan and 4Department of Environmental Oncology, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Kitakyushu 807-8555, Japan
We examined the replication fidelity of an Arg660Ser (R660S) mutant of Thermus aquaticus DNA polymerase I (Taq pol I). In a forward mutation assay, R660S showed a marked reduction in T
C transitions, one of the most frequent errors made by the wild-type enzyme. Steady-state kinetics showed that R660S discriminates against dGTP incorporation at a template T 13-fold better than the wild-type. R660S was also 3.2-fold less efficient than the wild-type at extending a T:dG mismatch. These results indicate that R660S has enhanced fidelity during incorporation and extension, which reduces its TC transition frequency. Interestingly, R660S also discriminated correct from incorrect nucleotides at the incorporation step of C:dATP, A:dATP, G:dATP and C:8-OH-dGTP mispairs 28-, 6.0-, 4.1- and 6.8-fold better, respectively, than the wild-type, although it may not always be as accurate as the wild-type at the extension step. A structural model suggests that Arg660 may participate in two interactions that influence fidelity; the guanidinium group of Arg660 might interact with the incoming guanine base at the major groove and it might compete for forming another interaction with the primer terminus. Substituting Arg with Ser may eliminate or alter these interactions and destabilize the closed complex with incorrect substrates. Our data also suggest that T:dGTP and C:dATP base pairs form ‘wobble’ structures at the incorporation step of Taq pol I.
* To whom correspondence should be addressed. Tel: +81 52 744 2456; Fax: +81 52 744 2457; Email: msuzuki{at}med.nagoya-u.ac.jp
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