DNA Topoisomerase 1

DNA Topoisomerase 1 releases the supercoiling and torsional tension of DNA introduced during DNA replication and transcription by transiently cleaving and rejoining one strand of the DNA duplex. It introduces a single-strand break via transesterification at a target site in duplex DNA. The scissile phosphodiester is attacked by the catalytic tyrosine of the enzyme, resulting in the formation of a DNA-(3'-phosphotyrosyl)-enzyme intermediate and the expulsion of a 5'-OH DNA strand. The free DNA strand than undergoes passage around the unbroken strand thus removing DNA supercoils. Finally, in the religation step, the DNA 5'-OH attacks the covalent intermediate to expel the active-site tyrosine and restore the DNA phosphodiester backbone By similarity. Regulates the alternative splicing of tissue factor (F3) pre-mRNA in endothelial cells.