Topoisomerase IV

Topoisomerase IV is one of two type-II topoisomerases in bacteria, the other being DNA gyrase. Like gyrase, topoisomerase IV is able to pass one double-strand of DNA through another double-strand of DNA, thereby changing the linking number of DNA by two in each enzymatic step.

Topoisomerase IV has two functions in the cell.

While topoisomerase IV does relax positive supercoils like DNA gyrase, it does not introduce further negative supercoiling like the latter enzyme.

Topoisomerase IV can unknot right-handed knots and decatenate right-handed catenanes without acting on right-handed plectonemes in negatively supercoiled DNA molecules, based on geometrical specificity of juxtapositions.

Topoisomerase IV is also a target of antibiotics, such as the quinolone drugs, which include ciprofloxacin.

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