The author's method of choice is secondary ion mass spectrometry (SIMS). Unlike previous X-ray–based techniques, SIMS yields the depth and localization information characteristic of the results from a confocal microscope. It does so by first using a laser to displace a thin, localized layer of the material under study, and then using mass spectrometry to analyze the displaced material. Strick et al. refine this technique to measure isotopes of a number of cations, but the most interesting results come in the measurements of Mg2+ and Ca2+. Both are associated with mitotic chromatin, but Mg2+ is evenly distributed across the chromatin, whereas Ca2+ is concentrated at the AT-rich axis of each chromosome. This mimics the localization of certain chromosome scaffold proteins, including topoisomerase II (Topo II).

Leading up to mitosis, Topo II is needed to cleave and allow...

You do not currently have access to this content.