BRCA1 and BLM co-localize at telomeres only in ALT cells and physically interact predominantly during G2.

(A) Quantitation of percent of cells with BLM-BRCA1, BRCA1-telomere, and BLM-BRCA1-telomere co-localized foci in Figure 3. (B) Upper panel: Co-immunoprecipitation of BLM with BRCA1 from U2OS cells. Cellular extracts (20 µg each) prepared at different stages of cell cycle were immunoprecipitated with an αBRCA1 antibody, separated on an 8% SDS-PAGE and analyzed by western blotting with αBLM antibody. Lower panel: Cellular extracts (20 µg each) used in upper panel corresponding to each stage were separated on an 8% SDS-PAGE and analyzed by western blotting with αLamin B antibody to show equivalent loading. The arrow mark indicates the position of BLM or Lamin B on the blot. Extracts from BLM-deficient cell line GM8505 served as a control.