Figure 4. HP1 facilitates KRAB/KAP1–mediated long-range repression.

(A) Two LV TrapSil-selected, tTRKRAB–expressing KAP1^−/− MEF clones were complemented by transduction with a lentiviral vector expressing either wild type KAP1 (KAP1^wt) or HP1 binding-defective KAP1 (KAP1^{R487E, V488E}), before FACS analysis in the presence or absence of dox. The mean fluorescence intensity values (MFI) of GFP and the silencing efficiency values are depicted as means of six independent measurements. The statistical analysis was performed using two-way ANOVA and, since the interactions were linked, the simple main effects were analyzed. The criterion for significance for all analyses was p<0.05. *: p<0.05. (B) Western blot analysis monitoring KAP1 protein levels, using PCNA as a loading control. The far right panel shows endogenous KAP1 expression in a MEF wild-type cell line.