As chromosomes prepare for division by the process of mitosis, they undergo reorganization into separate bodies. Through an RNAi screen, Daniel Gerlich and colleagues demonstrate that this process is mediated by Ki-67 — a protein known as a cell proliferation marker and used in cancer diagnostics. After nuclear envelope disassembly, Ki-67 prevents chromosomes from collapsing into a single cluster by acting as a biological surfactant. In fact, many biophysical properties of this protein match those of surfactants, and it appears to be through these properties, rather than though a specific region of the protein, that Ki-67 ensures chromosome separation.
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