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Fig. 4. Triple labeling of Ptk1 cells with autoimmune antibody to detect centromeres (A, D, G, J, M, and P), with antibody to topoisomerase II (B, E, H, K, N, and Q) and with the DNA stain DAPI (C, F, I, L, O, and R). Many interphase cells exhibit low or undetectable expression of topoisomerase II (AC). Cells in late G2 phase as evidenced by double centromere spots invariably show strong expression of topoisomerase II (DF). Prophase cells showed diffuse labeling of the chromosome arms with anti-topoisomerase II and a concentration at the centromeres (arrows; GI). During prometaphase, topoisomerase II was concentrated at the centromeres (arrows) and along the central axis of the chromosome arms (arrowhead; JL). Metaphase cells showed strong labeling of centromeres (arrows) and chromosome arms (MO). At late anaphase, the topoisomerase II was no longer highly concentrated at centromeres but was present on chromosome arms (PR). Bar, 5 µm.