Recombinosome Model: Rad51 and Dmc1 each form short filaments on both spatially separated ends of a DSB.

(Top) Short helical Rad51 and Dmc1 nucleoprotein homofilaments (green and red, respectively) form on adjacent segments of a single DSB-associated ssDNA tract. Each of these filaments is on the order of 100 nt or 33 protomers long and more than one Rad51-Dmc1 structure can form on a single tract of ssDNA. This single end of the DSB manifests itself cytologically as a side-by-side Rad51-Dmc1 co-focus (represented by the offset transparent red and green circles). (Left) Both Rad51 and Dmc1 similarly occupy the second end of the DSB. Prior to strand exchange, the two ends of the DSB are separated by 400 nm or less, resulting in focus pairing. The two ends of the DSB are both tethered to the axial element (purple box) by chromatin arms of variable length. Sister chromatids (pink circles) are often split in a DSB-independent manner. (Right) This architecture is maintained after strand exchange tethers the homolog at the predetermined distance of 400 nm or less.