PROSITE documentation PDOC00333
Prokaryotic DNA topoisomerase I active site


DNA topoisomerase I (EC [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 prokaryotic type I 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 5'-phosphate on DNA, at one end of the enzyme-severed DNA strand.

Prokaryotic organisms, such as Escherichia coli, have two type I topoisomerase isozymes: topoisomerase I (gene topA) and topoisomerase III (gene topB). Eukaroytes also contain homologs of prokaryotic topoisomerase III.

There are a number of conserved residues in the region around the active site tyrosine; we used this region as a signature pattern.

Last update:

December 2004 / Pattern and text revised.


Technical section

PROSITE method (with tools and information) covered by this documentation:

TOPOISOMERASE_I_PROK, PS00396; Prokaryotic DNA topoisomerase I active site  (PATTERN)


1AuthorsSternglanz R.
TitleDNA topoisomerases.
SourceCurr. Opin. Cell Biol. 1:533-535(1989).
PubMed ID2560656

2AuthorsSharma A. Mondragon A.
TitleDNA topoisomerases.
SourceCurr. Opin. Struct. Biol. 5:39-47(1995).
PubMed ID7773745

3TitleBjornsti M.-A.
SourceCurr. Opin. Struct. Biol. 1:99-103(1991).

4AuthorsRoca J.
TitleThe mechanisms of DNA topoisomerases.
SourceTrends Biochem. Sci. 20:156-160(1995).
PubMed ID7770916

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