“…Genetic studies quantitatively evaluating the kinetics of rejoining of radiation-induced DNA DSBs in wild type cells of higher eukaryotes [Dikomey and Franzke, 1986;Metzger and Iliakis, 1991], in mutants deficient in DNAPKcs [Nevaldine et al, 1997;DiBiase et al, 2000a], Ku [Wang et al, 2001b], or DNA ligase IV [Wang et al, 2001c], as well as after treatment with wortmannin [Wang et al, 2001a,b,c] provide evidence for the operation of at least two pathways of NHEJ with distinct properties that we have termed D-NHEJ and B-NHEJ [Wang et al, 2001b[Wang et al, , 2003] (see also ''Introduction''). D-NHEJ is fast (t 1/2 : 5-30 min), requires DNA-PKcs, Ku, DNA ligase IV, and probably Xrcc4 and rejoins DNA ends without excessive degradation [Wang et al, 2001b[Wang et al, , 2003].…”