Fig. 1. Anti-NBS1 and anti-NBS1-S(P)343 block the formation of RPA32-S(P)4-S(P)8 and RPA foci. (A-R) Following the introduction of the negative-control IgG (A-F), anti-NBS1 (G-L) or anti-NBS1-S(P)343 (M-R), HeLa cells were treated with 5 mM HU, or were mock-treated (control), for 3 hours. Cells were detergent-extracted and fixed, incubated with primary and secondary antibodies, and visualized by confocal microscopy. (D-F) HU treatment led to RPA32-S(P)4-S(P)8 (green) and RPA32 (red) focus formation in negative-control IgG-transfected cells. (J-L,P-R) anti-NBS1-and anti-NBS1-S(P)343-transfected cells contained RPA32 foci but RPA32-S(P)4-S(P)8 foci were not observed. HU-induced damage was verified by H2AX phosphorylation (supplementary material Fig. S4).