Fig. 4: BRCA2 recognizes G-triplex-derived intermediates.

a An experimental scheme to observe BRCA2OB binding towards the dual-labeled TelG5-G3 construct that mimics the G3 intermediate structure. smFRET histograms for b TelG5-G3 and c TelG5TTT-G3: DNA alone (top) and upon incubation with 1 μM BRCA2OB (bottom) with Gaussian fits (red). BRCA2OB-interacting states are filled in semi-transparent blue. Blue dashed line is the sum of the multiple Gaussian curves. One of the possible topologies of loop-associated G3:G4 (loop-G3:G4) and tail-associated G3:G4 (tail-G3:G4) are illustrated as a cartoon inside the histogram. Flanking tail sequences are underlined for each substrate at the top. d A schematic representation (left) of the molecular interaction between BRCA2OB and G4 structures during the direct NP-P transition. For reference, smFRET histograms of TelG5 (middle) and TelG5TTT (right) in the presence of 1 μM BRCA2OB from Fig. 2g and Supplementary Fig. 7, respectively, are shown (filled with gray). e EMSA to assess BRCA2OB binding to TelG5-G3, compared to TelG5 and TelG5TTT. TelG5GAG was employed as a negative control. Results are from the same gel. The experiments were repeated three times independently. f A model for BRCA2 binding to the G3 and G3:G4 intermediates during G4 conformational interconversions. Two possible G3:G4 conformations and one representative G3 structure that might form during the NP-P rearrangement without complete unfolding are shown. BRCA2 recognizes and binds to G3 intermediates, which reduce folding into G4.