Immunofluorescence analysis of DNA repair protein XRCC4 was performed using 70% confluent log phase U-87 MG cells. The cells were fixed with 4% paraformaldehyde for 10 minutes, permeabilized with 0.1% Triton™ X-100 for 15 minutes, and blocked with 2% BSA for 45 minutes at room temperature. The cells were labeled with XRCC4 Monoclonal Antibody (OTI4H9) (Product # MA5-24983) at 1:200 in 0.1% BSA, incubated at room temperature for 5 hours and then labeled with Donkey anti-Mouse IgG (H+L) Highly Cross-Adsorbed Secondary Antibody, Alexa Fluor Plus 488 (Product # A32766), (1:2,000), for 45 minutes at room temperature (Panel a: Green). Nuclei (Panel b:Blue) were stained with ProLong™ Diamond Antifade Mountant with DAPI (Product # P36962). F-actin (Panel c: Red) was stained with Rhodamine Phalloidin (Product # R415, 1:300). Panel d represents the merged image showing predominantly nuclear localization. Panel e represents control cells with no primary antibody to assess background. The images were captured at 60X magnification.