title: Evidence for the coupling of ATP hydrolysis to the final (extension) phase of RecA protein-mediated DNA strand exchange.
abstract: RecA protein promotes a limited DNA strand exchange reaction, without ATP hydrolysis, that typically results in formation of short (1-2 kilobase pairs) regions of hybrid DNA. This nascent hybrid DNA is extended in a reaction that can be coupled to ATP hydrolysis. When ATP is hydrolyzed, the extension phase is progressive and its rate is 380 +/- 20 bp min-1 at 37 degrees C. A single RecA nucleoprotein filament can participate in multiple DNA strand exchange reactions concurrently (involving duplex DNA fragments that are homologous to different segments of the DNA within a nucleoprotein filament), with no effect on the observed rate of ATP hydrolysis. The ATP hydrolytic and hybrid DNA extension activities exhibit a dependence on temperature between 25 and 45 degrees C that is, within experimental error, identical. This provides new evidence that the two processes are coupled. Arrhenius activation energies derived from the work are 13.3 +/- 1.1 kcal mole-1 for DNA strand exchange, and 14.4 +/- 1.4 kcal mole-1 for ATP hydrolysis during strand exchange. The rate of branch movement in the extension phase (base pair min-1) is related to the kcat for ATP hydrolysis during strand exchange (min-1) by a factor equivalent to 18 bp throughout the temperature range examined. The 18-base pair factor conforms to a quantitative prediction derived from a model in which ATP hydrolysis is coupled to a facilitated rotation of the DNA substrates. RecA filaments possess an intrinsic capacity for DNA strand exchange, mediated by binding energy rather than ATP hydrolysis, that is augmented by an ATP-dependent molecular motor.
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: W A
authors.initials: WA
authors.lastname: Bedale
authors.forename: M
authors.initials: M
authors.lastname: Cox
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D010584:Bacteriophage phi X 174; D002151:Calorimetry; D004270:DNA, Circular / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D004279:DNA, Viral / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D004926:Escherichia coli / Q000201:enzymology*; D006868:Hydrolysis; D007700:Kinetics; D008854:Microscopy, Electron; D008961:Models, Structural; D011938:Rec A Recombinases / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D004270:DNA, Circular; D004277:DNA, Single-Stranded; D004279:DNA, Viral; D000255:Adenosine Triphosphate; D011938:Rec A Recombinases