Twisting and untwisting a single DNA molecule covered by RecA protein

Publication Type:

Journal Article

Source:

BIOPHYSICAL JOURNAL, BIOPHYSICAL SOCIETY, Volume 87, Number 4, 9650 ROCKVILLE PIKE, BETHESDA, MD 20814-3998 USA, p.2552-2563 (2004)

DOI:

10.1529/biophysj.104.043059

Keywords:

ATP HYDROLYSIS; BINDING; COMPLEXES; DOUBLE-STRANDED DNA; DUPLEX DNA; ESCHERICHIA-COLI; FILAMENTS; POLYMERIZATION; STRUCTURAL TRANSITIONS; SUPERCOILED DNA

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.