Immunofluorescence
The cells cultured on cover slips were fixed with 2% paraformaldehyde and 2% sucrose in 1×PBS for 10 min and then permeabilized with 1% NP-40. After pre-incubation with 5% BSA/PBS, cells were incubated first with the primary antibody and then with the secondary antibody in 1% BSA/PBS for 1 h at room temperature. The slides were mounted with anti-fade mounting medium with DAPI (Solarbio). The primary antibodies used were anti-γH2AX (1:1000, Abcam), anti-DNA G-quadruplex (G4) antibody, clone 1H6 (1:200, Merck), anti-Blm (1:200, Invitrogen), anti-Recql4 (1:200, Invitrogen).