Probing DNA polymerase fidelity mechanisms using time-resolved fluorescence anisotropy.


Prior to undergoing postsynthetic 3'-5' editing (proofreading), a defective DNA primer terminus must be transferred from the 5'-3' polymerase active site to a remote 3'-5' exonuclease site. To elucidate the mechanisms by which this occurs, we have used time-resolved fluorescence spectroscopy to study the interaction of dansyl-labeled DNA primer/templates with the Klenow fragment of Escherichia coli DNA polymerase I. The dansyl probe is positioned such that when the DNA substrate occupies the polymerase active site, the probe is solvent-exposed and possesses a short average fluorescence lifetime (4.7 ns) and extensive angular diffusion (42.5 degrees). Conversely, when the DNA substrate occupies the exonuclease active site, the probe becomes buried within the protein, resulting in an increase in the average lifetime (14.1 ns) and a decrease in the degree of angular diffusion (14.4 degrees ). If both polymerase and exonuclease binding modes are populated (lower limit approximately 5%), their markedly different fluorescence properties cause the anisotropy to decay with a characteristic "dip and rise" shape. Nonlinear least-squares analysis of these data recovers the ground-state mole fractions of exposed (x(e)) and buried (x(b)) probes, which are equivalent to the equilibrium proportions of the DNA substrate bound at the polymerase and exonuclease sites, respectively. The distribution between the polymerase and exonuclease binding modes is given by the equilibrium partitioning constant K(pe) (equal to x(b)/x(e)). The important determinants of the proofreading process can therefore be identified by changes made to either the protein or DNA that perturb the partitioning equilibrium and hence alter the magnitude of K(pe).




new topics/pols set partial results complete validated


No results available for this paper.

Entry validated by:

Log in to edit reference All References

Using Polbase tables:


Tables may be sorted by clicking on any of the column titles. A second click reverses the sort order. <Ctrl> + click on the column titles to sort by more than one column (e.g. family then name).


It is also possible to filter the table by typing into the search box above the table. This will instantly hide lines from the table that do not contain your search text.