Figure 7.

RIF1 Represses DSB Resection Following IR and at the IgH Locus in Stimulated B Cells

(A and B) Enhanced ATR signaling in RIF1- and 53BP1-deficent cells. Lysates prepared from WT, Rif1^−/−, and 53Bp1^−/− MEFs, harvested at indicated time points following IR, were immunoblotted with indicated antisera.

(C) 53Bp1^−/− MEF lines reconstituted with indicated WT and mutant 53BP1 proteins (see also Figures 5A–5D) were examined for IR-induced checkpoint phosphorylation events as in (A) and (B).

(D) Lysates prepared from WT, Rif1^−/−, 53Bp1^−/−, and Rif1^−/−53Bp1^−/− MEFs harvested 3 hr following IR were immunoblotted with indicated antisera.

(E) Aberrant processing of the IgH locus in Rif1^−/− cells. Schematic of IgH Sμ region shows relative positions of qPCR amplicons used in ChIP experiments. A control non-IgH locus (Rpp30) was also examined. Resting B cells or those stimulated with LPS and IL-4 (72 hr) were subjected to ChIP experiments with IgG (control), histone H2A.X, and RPA32 monoclonal antisera. Following background subtraction of IgG signals, values were normalized to the DNA input signals, followed by the maximum value in each data set. Mean signals, two independent experiments ± SEM. See also Figure S7.