Normal G-strand overhang in Ku86−/−-deficient primary cells. G-strand overhangs in fresh BM cells or primary MEFs, as indicated, from littermate wild-type and DNA-PKcs−/− mice were visualized in native gel after hybridization with a (CCCTAA)4 probe (see Materials and Methods). Notice that upon treatment with two different doses of MBN (40 and 100 U) the G-strand-specific signal decreases. As a control, the same gel was denatured and reprobed with the (CCCTAA)4 probe to visualize telomeres. DA40 and DA39 are littermate wild-type and DNA-PKcs−/− mice, respectively. B3, B4, B5, and B6 are primary MEF cultures from littermates, as are C2, C3, C5, and C9. See Table 5 for quantification of G-strand-specific signals. HMW, high molecular weight.