DNA2 processes stalled replication forks. (A, top) DNA2 expression after siRNA knockdown. (bottom) Colony-forming assays in control and DNA2-depleted U-2 OS cells treated with 4 mM HU for the indicated time. (B) Representative IdU tracts in DNA2 conditional knockout HCT116 cells (out of two repeats). Tamoxifen was added to generate conditional knockout cells (see Materials and methods). (C, left) Expression of DNA2 and RECQ1 in tamoxifen-treated HCT116 cells. Right, representative IdU tracts in DNA2 conditional knockout HCT116 cells depleted for Luc or RECQ1 (out of three repeats). n ≥ 300 tracts scored for each dataset shown in B and C.