DNA topoisomerase I, mitochondrial (Top1mt)

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

The scissile phosphodiester is attacked by the catalytic tyrosine of this 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 whole phosphodiester bond on the opposing strand, thus removing DNA supercoils.