Visualization of DNA Topoisomerases by Electron Microscopy
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Eukaryotic DNA Topoisomerase II (Topo II) is an essential enzyme that catalyzes the relaxation of supercoiled DNA and the segregation of newly replicated chromosomes (1 -3 ). The enzyme is highly conserved through evolution, and appears to result from the fusion of the A- and B-subunits of bacterial DNA gyrase (4 ). It has an A2 dimeric structure, whereas the bacterial enzyme has an A2 B2 tetrameric arrangement.
