Operationally, topoisomerase IV is a type II topoisomerase required for the decatenation step of chromosome segregation. Not every bacterium has both a topo II and a topo IV. The topo IV families of the Gram-positive bacteria and the Gram-negative bacteria appear not to represent a single clade among the type II topoisomerases, and are represented by separate models for this reason. [DNA metabolism, DNA replication, recombination, and repair]
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