PMID:12527299
| Citation |
Maluf, NK, Fischer, CJ and Lohman, TM (2003) A Dimer of Escherichia coli UvrD is the active form of the helicase in vitro. J. Mol. Biol. 325:913-35 |
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| Abstract |
The Escherichia coli UvrD protein is a 3' to 5' SF1 DNA helicase involved in methyl-directed mismatch repair and nucleotide excision repair of DNA. We have characterized in vitro UvrD-catalyzed unwinding of a series of 18 bp duplex DNA substrates with 3' single-stranded DNA (ssDNA) tails ranging in length from two to 40 nt. Single turnover DNA-unwinding experiments were performed using chemical quenched flow methods, as a function of both [UvrD] and [DNA] under conditions such that UvrD-DNA binding is stoichiometric. Although a single UvrD monomer binds tightly to the single-stranded/double-stranded DNA (dsDNA) junction if the 3' ssDNA tail is at least four nt, no unwinding was observed for DNA substrates with tail-lengths </=8 nt, even at high [UvrD]/[DNA] ratios. Unwinding is observed for DNA substrates with 3' ssDNA tail lengths >/=12 nt, and the unwinding amplitude displays a sigmoidal dependence on [UvrD(tot)]/[DNA(tot)]. Quantitative analysis of these data indicates that a single UvrD monomer bound at the ssDNA/dsDNA junction of any DNA substrate, independent of 3' ssDNA tail length, is not competent to fully unwind even a short 18 bp duplex DNA, and that two UvrD monomers must bind the DNA substrate in order to form a complex that is able to unwind short DNA substrates in vitro. Other proteins, including a mutant UvrD with no ATPase activity as well as a monomer of the structurally homologous E.coli Rep helicase, cannot substitute for the second UvrD monomer, suggesting a specific interaction between two UvrD monomers and that both must be able to hydrolyze ATP. Initiation of DNA unwinding in vitro appears to require a dimeric UvrD complex in which one subunit is bound to the ssDNA/dsDNA junction, while the second subunit is bound to the 3' ssDNA tail. |
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| Keywords |
Adenosine Triphosphatases/chemistry; Adenosine Triphosphatases/deficiency; Adenosine Triphosphatases/genetics; Adenosine Triphosphatases/isolation & purification; Adenosine Triphosphatases/metabolism; Adenosine Triphosphate/pharmacology; Binding, Competitive; Capsid/physiology; Capsid Proteins; DNA/metabolism; DNA Helicases/chemistry; DNA Helicases/deficiency; DNA Helicases/genetics; DNA Helicases/isolation & purification; DNA Helicases/metabolism; DNA, Bacterial/metabolism; DNA, Single-Stranded/metabolism; Dimerization; Escherichia coli/enzymology; Escherichia coli/genetics; Escherichia coli Proteins; Kinetics; Mathematics; Protein Binding; Temperature; Ultracentrifugation |
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