Fig 1: TNKS loads the BRCA1A complex on chromatin.(A) TNKS tethering to the lacO array leads to MERIT40 and RAP80 binding in a PARP activity independent manner even in the absence of DSBs. U2OS17 cells were transfected with GFP-lacR, GFP-lacR-TNKS1 or the PARP activity mutant version: GFP-lacR-TNKS1mut. ISce-I was co-transfected to induce pure DSBs at the lacO array. Immunofluorescence staining was performed to visualize the localization pattern of MERIT40 or RAP80 in the cells. The values represent the results of three independent experiments with SD (N = 100). On the right representative confocal microscopy pictures are shown. (B) The recruitment of MERIT40 and RAP80 is affected in TNKS1/2 knock down cells. U2OS17 cells were transfected with the indicated siRNAs. After depletion, cells were transfected with mCherry-lacR and ISce-I where indicated. Immunofluorescence staining was performed to visualize Merit40 or RAP80 in the cells. Relative values compared to the control are the results of three independent experiments with SD (N = 100 cells in each condition). (C) TNKS depleted cells are deficient for RAP80 foci formation. U2OS cells were transfected with siRNAs as shown and treated with NCS 48 hours later. The frequency of foci-positive cells was determined in three independent experiments (N = 100) and is shown as relative to the control (D) MDC1-mediated TNKS recruitment is necessary for efficient binding of the BRCA1 complex to DSBs in vivo. U2OS17 cells were transfected with mCherry-lacR-MDC1 wt or its TBD mutant version and ISce-I. Percent of cells harboring MERIT40 or RAP80 signal on the array was determined after immunofuorescence staining. Results from three independent experiments are shown with SD (N = 100) as relative frequencies compared to control. (E) MERIT40 stabilizes BRCA1 on the TNKS-bound chromatin. Control or MERIT40 depleted U2OS17 cells were transfected with GFP-lacR, GFP-lacR-TNKS1, GFP-lacR-TNKS1mut and ISce-I. Percent of cells harboring BRCA1 signal on the array was determined. Results from three independent experiments are shown with SD (N = 100).