Topo IIα localizes to the axial core of M. muntjak mitotic chromosomes. (A) GFP–human Topo IIα transfected into M. muntjak cells does not coimmunoprecipitate with endogenous M. muntjak Topo IIα when precipitated using an anti-GFP antibody (right). GFP–human Topo IIα ΔCTR (i.e., amino acids 1–1,321) transfected into HeLa cells and immunoprecipitated in the same way coprecipitates the endogenous, untagged protein (left). (The anti–Topo IIα antibody used for Western blotting recognizes only WT human or M. muntjak Topo IIα and not Topo IIα ΔCTR.) (B) Human Topo IIα localization in M. muntjak cells transfected with a construct encoding GFP–Topo IIα, fixed and stained with DAPI, demonstrating densely punctate localization of GFP–Topo IIα to the axial core of mitotic chromosomes (bottom) and nuclear localization during interphase (top). Bars, 10 µm. (See also Video 1.) (C, left) Enlarged portion of region marked by the broken-line box in B to show apparent coiling of the axial core. (C, right) A representative (more than three experimental repeats) plot across mitotic chromosome arms showing that the GFP signal (Topo IIα) occupies a narrower region than the DNA (DAPI) signal (corresponds to the solid boxed region in B). Bars, 1 µm.