Kinetic Measurement of the Step Size of DNA Unwinding by Escherichia coli UvrD Helicase

The kinetic mechanism by which the DNA repair helicase UvrD of Escherichia coli unwinds duplex DNA was examined with the use of a series of oligodeoxynucleotides with duplex regions ranging from 10 to 40 base pairs. Single-turnover unwinding experiments showed distinct lag phases that increased with...

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Veröffentlicht in:	Science (American Association for the Advancement of Science) 1997-01, Vol.275 (5298), p.377-380
Hauptverfasser:	Ali, Janid A., Lohman, Timothy M.
Format:	Artikel
Sprache:	eng
Schlagworte:	Adenosine Triphosphatases - metabolism Adenosine Triphosphate - metabolism Analytical estimating Bacteria Base Composition Biochemistry Biological and medical sciences Biophysics Deoxyribonucleic acid Dimers DNA DNA - chemistry DNA - metabolism DNA Helicases - metabolism DNA repair DNA topoisomerase I DNA, Single-Stranded - metabolism Escherichia coli Escherichia coli - enzymology Escherichia coli Proteins Fundamental and applied biological sciences. Psychology Gels Genetic aspects Kinetics Least squares Molecular and cellular biology Molecular genetics Molecules Monomers Mutagenesis. Repair Nucleic Acid Conformation Oligodeoxyribonucleotides - chemistry Oligodeoxyribonucleotides - metabolism Physiological aspects Topoisomerase I
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Zusammenfassung:	The kinetic mechanism by which the DNA repair helicase UvrD of Escherichia coli unwinds duplex DNA was examined with the use of a series of oligodeoxynucleotides with duplex regions ranging from 10 to 40 base pairs. Single-turnover unwinding experiments showed distinct lag phases that increased with duplex length because partially unwound DNA intermediate states are highly populated during unwinding. Analysis of these kinetics indicates that UvrD unwinds duplex DNA in discrete steps, with an average "step size" of 4 to 5 base pairs (approximately one-half turn of the DNA helix). This suggests an unwinding mechanism in which alternating subunits of the dimeric helicase interact directly with duplex DNA.
ISSN:	0036-8075 1095-9203
DOI:	10.1126/science.275.5298.377