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Fig. 5. Triple labeling of Ptk1 cells with human autoimmune serum to identify centromeres (A, D, G, J, M, P, and S) with anti-topoisomerase IIß antibody (B, E, H, K, N, Q, and T) and with DAPI for DNA (C, F, I, L, O, R, and U). Topoisomerase IIß was expressed in all interphase cells, whether they had single (A–C) or doubled (D–F) centromere spots. Prophase cells showed inhomogeneous nuclear labeling with anti-topoisomerase IIß with concentration near sites of chromosome condensation (G–I). By prometaphase, topoisomerase IIß was predominately detected closely associated with the mitotic chromosomes (J–L). At metaphase, topoisomerase IIß was found on chromosomes with only a slight tendency to concentrate at centromeres (arrows; M–O). At anaphase, topoisomerase IIß was distributed along chromosome arms (P–R). In telophase cells, topoisomerase IIß remained associated with chromosomes during chromosome decondensation (S–U). Bar, 5 µm.