biotinylated -dna and fluorescently labeled human rad51 ( isoform q313 ) were prepared as described elsewhere . atp hydrolysis was triggered in the flow cell by exposing the trapped rad51-dsdna complex to a buffer containing 10 mm mg and 10 mm egta . descriptions of the combined dual optical tweezers and fluorescence microscope as well as data analysis procedures are provided in the supplementary information and supplementary figs . s1s3 .
the central catalyst in eukaryotic atp - dependent homologous recombination consists of rad51 proteins , polymerized around single - stranded dna . 
 this nucleoprotein filament recognizes a homologous duplex dna segment and invades it1,2 . after strand exchange , 
 the nucleoprotein filament should disassemble in order for the recombination process to complete3 . 
 the molecular mechanism of rad51 filament disassembly is poorly understood . here 
 , we have combined optical tweezers with single - molecule fluorescence microscopy and microfluidics4,5 to reveal that disassembly results from the interplay between atp hydrolysis and release of the tension stored in the nucleoprotein filament . applying external tension to the dna 
 , we found that disassembly slows down and can even be stalled . 
 we quantified the fluorescence of rad51 patches and found that disassembly occurs in bursts interspersed by long pauses . upon relaxation of a stalled complex , pauses were suppressed resulting in a large burst . 
 these results imply that tension - dependent disassembly takes place only from filament ends , after tension - independent atp hydrolysis . 
 this integrative single - molecule approach allowed us to dissect the mechanism of this key homologous recombination reaction step , which in turn clarifies how disassembly can be influenced by accessory proteins .