Elastic Behavior of RecA-DNA Helical Filaments

Escherichia coli RecA protein forms a right-handed helical filament with DNA molecules and has an ATP-dependent activity that exchanges homologous strands between single-stranded DNA (ssDNA) and duplex DNA. We show that the RecA–ssDNA filamentous complex is an elastic helical molecule whose length is controlled by the binding and release of nucleotide cofactors. RecA–ssDNA filaments were fluorescently labelled and attached to a glass surface inside a flow chamber. When the chamber solution was replaced by a buffer solution without nucleotide cofactors, the RecA–ssDNA filament rapidly contracted approximately 0.68-fold with partial filament dissociation. The contracted filament elongated up to 1.25-fold when a buffer solution containing ATPγS was injected, and elongated up to 1.17-fold when a buffer solution containing ATP or dATP was injected. This contraction–elongation behavior was able to be repeated by the successive injection of dATP and non-nucleotide buffers. We propose that this elastic motion couples to the elastic motion and/or the twisting rotation of DNA strands within the filament by adjusting their helical phases.