Twisting and untwisting a single DNA molecule covered by RecA protein |
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Authors: | Fulconis Renaud Bancaud Aurélien Allemand Jean-Francois Croquette Vincent Dutreix Marie Viovy Jean-Louis |
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Affiliation: | Laboratoire Physico-Chimie Curie, UMR CNRS 168, Institut Curie, Paris, France. |
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Abstract: | We study dsDNA-RecA interactions by exerting forces in the pN range on single DNA molecules while the interstrand topological state is controlled owing to a magnetic tweezers setup. We show that unwinding a duplex DNA molecule induces RecA polymerization even at moderate force. Once initial polymerization has nucleated, the extent of RecA coverage still depends on the degree of supercoiling: exerting a positive or negative torsional constraint on the fiber forces partial depolymerization, with a strikingly greater stability when ATPgammaS is used as a cofactor instead of ATP. This nucleofilament's sensitivity to topology might be a way for the bacterial cell to limit consumption of precious RecA monomers when DNA damage is addressed through homologous recombination repair. |
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