Assembly and Disassembly of RecA Protein Filaments Occur at Opposite Filament Ends RELATIONSHIP TO DNA STRAND EXCHANGE*

RecA protein primarily associates with and disso-ciates 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 depolym-erization at the other end drives unidirectional strand exchange. There is no demonstrable correlation be-tween 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’-0-(3-thiotriphos