DNA topoisomerase 1 (TOP1)

Releases the supercoiling and torsional tension of DNA introduced through the DNA replication and transcription by transiently cleaving and rejoining one strand of the DNA duplex. Introduces a single-strand break through transesterification in a target site in duplex DNA.

The scissile phosphodiester is assaulted by the catalytic tyrosine of the enzyme, leading to the formation of a DNA-(3'-phosphotyrosyl)-enzyme intermediate and the expulsion of a 5'-OH DNA strand. The free DNA strand then rotates around the intact phosphodiester bond on the opposing strand, thus removing DNA supercoils.