Fig. 4. Ectopic expression of Orc1 induced DNA fragmentation similar to non-transfected cells that spontaneously over-expressed Orc1. (A) Non-transfected CHO cells were stained with Hoechst to stain DNA (blue), with TUNEL assay to label double-stranded DNA breaks (green), and with anti-FLAG antibody to label FCgOrc1 (red; F-Orc). DIC, differential interference contrast. (B) CHO cells were transfected with 1 µg of either pFCgOrc1 (F-Orc1) or pFCgOrc2 (F-Orc2). At 18 hours post-transfection, the attached cells were treated as in panel A. (C) Same as in panel B, except that attached cells were analyzed at 36 hours post-transfection, and pCI-transfected cells were included. In the merged images, yellow indicates sites where DNA breaks and Orc were co-localized, and white indicates sites where DNA and Orc1 were co-localized.