FIGURE 3.

ETEs are generated by hairpin-capped DNA in an IR-dependent fashion. Supercoiled, linear, or hairpin-capped pΔBM-d2EGFP (A) and pSFVdhfr or pSFV-V (B) were prepared as shown in Fig. 1. For the latter plasmids, the DNA was hairpin-capped at both ends or a single end. DNA was transfected into COLO 320DM cells, and after 1 month, the plasmid sequences in stable transformants were analyzed by FISH. Plasmid signals in interphase nuclei are classified as large (L) or small (S) HSRs, DMs, and few (+) or many (++) ETEs, as shown in Fig. 2 (A–F). The frequency of cells bearing each structure was determined by viewing more than 500 interphase nuclei.