Rl 610 132 121

FLAG-BLM was incubated with biotinylated EXO1, two units of DNase I (NEB), and 20 ng of bovine serum albumin (BSA, Fisher Scientific) in Buffer A (25 mM Tris-HCl [pH 8.0], 100 mM NaCl, and 10% glycerol) for 30 minutes on ice. The samples were then added to a mixture of 100 ng BSA and 5 μL of streptavidin-coated paramagnetic beads (Dynabeads M-280, Life Tech.) for an additional 15 min incubation on ice. After three washes with 2 mg mL⁻¹ BSA in Buffer A, proteins bound to the beads were resolved by 8% SDS-PAGE, followed by western blotting with anti-FLAG primary antibodies (Sigma-Aldrich, F1804), anti-mouse secondary antibodies (Rockland, RL-610-132-121), and streptavidin ATTO647N (Atto-Tec, AD 647N-65).

Triple flag-Mre11-Rad50-Nbs, Mre11-flag, Rad50ΔCC-HA, or Nbs1-flag were each incubated with biotinylated hExo1, two units of DNase I (NEB), and 20 ng of bovine serum albumin (BSA, Fisher Scientific) in A buffer (25 mM Tris-HCl [pH 8.0], 100 mM NaCl, and 10% glycerol) for 30 minutes on ice. The samples were then added to a mixture of 100 ng BSA and 5 μL of Dynabeads M-280 Streptavidin (Life Tech) for additional 15 min incubation on ice. After three washes with 2 mg mL⁻¹ BSA in A buffer, proteins bound to the beads were resolved by 8% SDS-PAGE, followed by Western blotting with anti-flag primary antibody (Sigma-Aldrich, F1804-1MG) or anti-HA primary antibody (GeneTex, GTX18181), anti-mouse secondary antibody (Rockland, RL-610-132-121), and streptavidin atto647N (Atto-Tec, AD 647N-65).