Chromatin unfolding by tethered DDB2 requires PARP activity and ATP hydrolysis. (A–D) Human U2OS 2–6-3 cells containing 200 copies of a LacO-containing cassette (∼4 Mbp) were transfected with mCherry-LacR-DDB2 in the presence of IPTG. Cells were subsequently released for the indicated time points in medium containing DMSO (A) or 1 µM PARP inhibitor (B) or in regular medium followed by a 30-min incubation in mock medium (C) or ATP depletion medium (D). The lookup table for the color coding is shown. (E) Quantitative measurements on the relative size of the array (surface of the array/surface of the nucleus) in cells subjected to the indicated conditions (30–50 cells for each condition collected in two independent experiments) are shown in a box plot. Open circles are data points that are considered outliers, as their value is greater than the upper quartile, +1.5 the interquartile distance, or less than the lower quartile, −1.5 the interquartile distance. depl., depleted; PARPi, PARP inhibitor.