Fig. 1: The BRCA2 OB-folds binds to telomeric G-quadruplexes.

a Schematic illustration of human BRCA2. BRC repeats, OB folds, and the nuclear localization signal (NLS) are marked. Recombinant BRCA2 OB-folds domain (2665-3197 a.a.; BRCA2OB), tagged with N-terminal MBP was purified (SDS-PAGE gel at right). b Electrophoresis mobility shift assay (EMSA) was used to assess binding of recombinant BRCA2OB to telomere repeats. TelG5, G-rich single-stranded (GGTTAG)₅ repeats; TelC5, C-rich strand complementary to TelG5; TelG5:TelC5, double-stranded. ³²P-labeled hot probe is marked with an asterisk(*). Arrow marks the BRCA2OB-bound hot probe. c Increasing concentrations of BRCA2OB were incubated with TelG5 (lanes 2 to 4). Binding specificity was confirmed by competing with 1000X excess of unlabeled TelG5 (+, Cold TelG5, lane 5) and Poly(dI-dC) for negative control (lane 6). d Single-stranded (ss) telomeric repeat oligonucleotides of increasing length (TelG3 – TelG6, see illustration at the top) were incubated with (+) or without (-) BRCA2OB and subjected to EMSA. The binding of BRCA2OB to telomere repeats was detected from TelG5 and TelG6. e BRCA2OB specifically binds to TelG5, which forms the G-quadruplex (G4), but not to the single-stranded mutant (TelG5GAG). f A G4 ligand PDS challenges the binding of BRCA2OB to G4 in a dose-dependent manner. EMSA analyses were performed in the presence of 100 mM KCl. All experiments were repeated more than three times independently.