InterPro domain: IPR025834

DNA topoisomerase I ( 5.99.1.2 ) [ 1 , 2 , 3 , 4 ] is one of the two types of enzyme that catalyze the interconversion of topological DNA isomers. Type I topoisomerases act by catalyzing the transient breakage of DNA, one strand at a time, and the subsequent rejoining of the strands. When a eukaryotic type 1 topoisomerase breaks a DNA backbone bond, it simultaneously forms a protein-DNA link where the hydroxyl group of a tyrosine residue is joined to a 3'-phosphate on DNA, at one end of the enzyme-severed DNA strand. In eukaryotes and poxvirus topoisomerases I, there are a number of conserved residues in the region around the active site tyrosine [ 5 ].

This domain is found at the C terminus of topoisomerase I.

1. DNA topoisomerases. Curr. Opin. Cell Biol. 1, 533-5
2. DNA topoisomerases. Curr. Opin. Struct. Biol. 5, 39-47
3. Peptide sequencing and site-directed mutagenesis identify tyrosine-727 as the active site tyrosine of Saccharomyces cerevisiae DNA topoisomerase I. Proc. Natl. Acad. Sci. U.S.A. 86, 3559-63
4. The mechanisms of DNA topoisomerases. Trends Biochem. Sci. 20, 156-60