Abstract
RecA protein primarily associates with and dissociates from opposite ends of nucleoprotein filaments formed on linear duplex DNA. RecA nucleoprotein filaments that are hydrolyzing ATP therefore engage in a dynamic process under some conditions that has some of the properties of treadmilling. We have also investigated whether the net polymerization of recA protein at one end of the filament and/or a net depolymerization at the other end drives unidirectional strand exchange. There is no demonstrable correlation between recA protein association/dissociation and the strand exchange reaction. RecA protein-mediated DNA strand exchange is affected minimally by changes in reaction conditions (dilution, pH shift, or addition of small amounts of adenosine-5'-O-(3-thiotriphosphate) that have large and demonstrable effects on recA protein association, dissociation, or both. Rather than driving strand exchange, these assembly and disassembly processes may simply represent the mechanism by which recA nucleoprotein filaments are recycled in the cell.
Highlights
RecA protein primarily associates with and dissociates from opposite ends of nucleoprotein filaments formed on linear duplex DNA
We show that recA protein primarily associates with and dissociates from opposite ends of a nucleoprotein filament on dsDNA
The percentage of DNA bound by recA protein at a given time can be estimated by dividing the rate of ATP hydrolysis at that time by the rate observed at saturation
Summary
The recA protein of Escherichia coli promotes key steps in homologous recombination and recombinational DNA repair (for reviews, see Cox and Lehman, 1987; Kowalczykowski, 1987; Griffith and Harris, 1988; Radding, 1988). These processes are mimicked in uitro by recA protein-mediated DNA strand exchange reactions.
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