SMARCAL1 functions at stalled replication forks. (A,B) U2OS cells were transfected with a SMARCAL1 expression vector then fixed and stained with the indicated antibodies and appropriate fluorophore-conjugated secondary antibodies. In A, the cells were pulsed with BrdU for 20 min prior to staining. (C,D) U2OS cells transfected with siRNA targeting CHK1 or SMARCAL1 were stained with antibodies to γH2AX and cyclin A. Cells were scored as positive for one or both proteins by immunofluorescence imaging. Nontransfected cells were also irradiated with 5 Gy of IR for comparison. (E–G) U2OS cells were transfected with a GFP-SMARCAL1 expression vector, then fixed and stained. Staining in F is as follows: (Panels 1–4) SMARCAL1 (green) and BrdU (red); (panels 5–8) SMARCAL1 (green) and RPA (red); (panels 9–12) SMARCAL1 (green) and PCNA (red). Panels 3, 7, and 11 are merged images, and panels 4, 8, and 12 were stained with DAPI. In G, the cells containing SMARCAL1 localized to foci were scored after addition of 2 mM HU. (H) Localization of endogenous SMARCAL1 was examined by indirect immunofluorescence with affinity-purified anti-SMARCAL1 antibody in HU or UV radiation-treated U2OS cells. These cells also stably express HA-ATRIP, which permitted analysis of colocalization using anti-HA monoclonal antibody. Specificity of the SMARCAL1 antibody was confirmed in SMARCAL1-silenced cells. (Unt) Untreated. Cells were extracted with Triton X-100 prior to staining, so only chromatin-bound SMARCAL1 is observed. (I) The percentage of cells containing endogenous SMARCAL1 in foci was scored in cells treated with HU for the indicated times. Error bars in all graphs are standard deviation (n = 3).