Abstract:
:High-level quantum-chemical and quantum-dynamics calculations are reported on the tautomerization equilibrium and rate constants of guanine and its complexes with one and two water molecules. The results are used to estimate the fraction of guanine present in the cell during DNA synthesis as the unwanted tautomer that forms an irregular base pair with thymine, thus giving rise to a spontaneous GC --> AT point mutation. A comparison of the estimated mutation frequency with the observed frequency in Escherichia coli is used to analyze two proposed mechanisms, differing in the extent of equilibration reached in the tautomerization reaction. In the absence of water, the equilibrium concentration of tautomeric forms is relatively large, but the barrier to their formation is high. If water is present, tautomeric forms are less favored, but water molecules may serve as efficient proton conduits causing rapid tautomerization. It is tentatively concluded that the mechanism in which a high tautomerization barrier keeps the tautomeric transformation far from a state of equilibrium is more likely than a mechanism in which water and/or polymerases produce a low equilibrium concentration of the tautomeric forms.
journal_name
Biopolymersjournal_title
Biopolymersauthors
Gorb L,Podolyan Y,Leszczynski J,Siebrand W,Fernández-Ramos A,Smedarchina Zdoi
10.1002/1097-0282(2001)61:1<77::AID-BIP10062>3.0.Csubject
Has Abstractpub_date
2001-01-01 00:00:00pages
77-83issue
1eissn
0006-3525issn
1097-0282pii
10.1002/1097-0282(2001)61:1<77::AID-BIP10062>3.0.Cjournal_volume
61pub_type
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