Probing Rad51-DNA interactions by changing DNA twist.

In eukaryotes, Rad51 protein is responsible for the recombinational repair of double-strand DNA breaks. Rad51 monomers cooperatively assemble on exonuclease-processed broken ends forming helical nucleo-protein filaments that can pair with homologous regions of sister chromatids. Homologous pairing allows the broken ends to be reunited in a complex but error-free repair process.

Direct observation of twisting steps during Rad51 polymerization on DNA.

The human recombinase hRad51 is a key protein for the maintenance of genome integrity and for cancer development. Polymerization and depolymerization of hRad51 on duplex DNA were studied here using a new generation of magnetic tweezers, measuring DNA twist in real time with a resolution of 5 degrees . Our results combined with earlier structural information suggest that DNA is somewhat less extended by hRad51 than by RecA (4.

Real-time measurements of the nucleation, growth and dissociation of single Rad51-DNA nucleoprotein filaments.

Human Rad51 (hRad51), the protein central to DNA pairing and strand exchange during homologous recombination, polymerizes on DNA to form nucleoprotein filaments. By making use of magnetic tweezers to manipulate individual DNA molecules, we measured the nucleation and growth of hRad51 nucleoprotein filaments, and their subsequent disassembly in real time. The dependence of the initial polymerization rate upon the concentration of hRad51 suggests that the rate-limiting step is the formation of a nucleus involving 5.