Fig. 1. Dissociation of recombination intermediates by WRN. (A) Schematic diagram indicating recombination intermediates (α-structures) and the expected products of branch migration. A region of heterology (1670 bp) at the distal end of the linear duplex blocks strand exchange and is represented by a filled box. The positions of the ³²P-labels are indicated with asterisks. (B) Activity of WRN protein on recombination intermediates. Purified recombination intermediates (1.5 µM, expressed as a concentration of nucleotide residues) were incubated with: lane a, 200 nM RuvA and 100 nM RuvB; lanes c–g, 0.7–10.5 nM WRN; lanes i–m, 5.2 nM WRN and RuvA as indicated. In the reactions indicated, purified recombination intermediates were pre-incubated for 3 min on ice with RuvA before addition of WRN. The positions of the recombination intermediates (α) and linear duplex DNA (L) are indicated.