Nucleoside triphosphate binding to DNA polymerase III holoenzyme of Escherichia coli. A direct photoaffinity labeling study.


The physical basis of ATP binding and activation of DNA polymerase III ...
The physical basis of ATP binding and activation of DNA polymerase III holoenzyme was studied by an ultraviolet irradiation cross-linking technique. ATP and dATP were photocrosslinked to the alpha, tau, gamma, and delta subunits of holoenzyme; photocrosslinking of dATP was competitively inhibited by ATP. No photocrosslinking was observed with GTP or CTP, nor did GTP, CTP, or UTP inhibit cross-linking of ATP. ADP and adenosine 5'-O-(3-thio)-triphosphate, both potent inhibitors of ATP activation of holoenzyme, inhibited cross-linking of ATP to tau, gamma, and delta subunits, but not to the alpha subunit, suggesting that one or more of these subunits are ATP (or dATP)-binding sites. Photocrosslinking of dTTP to the ATP-activated holoenzyme was exclusively to the epsilon subunit, the dnaQ ( mutD ) gene product; dCTP and dGTP were not photocrosslinked to any subunit. Binding of dTTP was enhanced by ATP, but by no other nucleotide (or deoxynucleotide). This binding of dTTP to epsilon, a subunit likely responsible for regulation of proofreading by the holoenzyme, may function in the control of the fidelity of replication.






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