Cocrystal structure of an editing complex of Klenow fragment with DNA.


High-resolution crystal structures of editing complexes of both duplex and single-stranded DNA bound to Escherichia coli DNA polymerase I large fragment (Klenow fragment) show four nucleotides of single-stranded DNA bound to the 3'-5' exonuclease active site and extending toward the polymerase active site. Melting of the duplex DNA by the protein is stabilized by hydrophobic interactions between Phe-473, Leu-361, and His-666 and the last three bases at the 3' terminus. Two divalent metal ions interacting with the phosphodiester to be hydrolyzed are proposed to catalyze the exonuclease reaction by a mechanism that may be related to mechanisms of other enzymes that catalyze phospho-group transfer including RNA enzymes. We suggest that the editing active site competes with the polymerase active site some 30 A away for the newly formed 3' terminus. Since a 3' terminal mismatched base pair favors the melting of duplex DNA, its binding and excision at the editing exonuclease site that binds single-stranded DNA is enhanced.



Structure and Structure/Function


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Polymerase Reference Property Result Context
Klenow fragment Freemont PS1988 Residues Involved in Catalysis of 3-5' Exo D355, E357, D424, D501
Klenow fragment Freemont PS1988 Other Important Residues L361, Q419, R455, F473, Y497, H660

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