Lig4 depletion does not increase Chk1 or Chk2 phosphorylation or dephosphorylation. pChk1 (Ser317 or Ser345), pChk2 (Thr68), total Chk1, or total Chk2 were assessed via western blot. The experiment was repeated three times. (a, c) Lig4 depleted or scrambled control treated (NT) cells were treated with 10 mM hydroxyurea or PBS for 1 or 24 hr. (b, d) Lig4 depleted or NT cells were treated with 10 mM HU or PBS for 1 hr and released for indicated times.