Figure 3.

NHEJ and HR at two-ended DSBs in G2. Two-ended DSBs arising in G2 phase can be repaired by fast resection-independent NHEJ and slow HR. NHEJ is potentially error-prone since it cannot reconstitute sequence information that is lost at the break site. HR is error-free if the homologous sequence on the sister chromatid is used. However, HR can cause COs which are deleterious if it involves a homologous template other than the sister chromatid or if the sister chromatid is used off-frame, e.g. at repetitive sequences. Thus, both processes are potentially error-prone. Moreover, the G2/M checkpoint which serves to provide time for repair is negligent and allows cells to progress into mitosis with unrepaired DSBs. Thus, it might be beneficial for a cell to use fast NHEJ instead of slow HR to repair as many breaks as possible.