InterPro domain: IPR034144

This topoisomerase-primase (TOPRIM) domain is found in members of the type IA family of DNA topoisomerases (Topo IA) similar to topoisomerase III. Type IA DNA topoisomerases remove (relax) negative supercoils in the DNA by cleaving one strand of the DNA duplex, covalently linking to the 5' phosphoryl end of the DNA break, and allowing the other strand of the duplex to pass through the gap [ 1 ]. Esherichia coli harbours two type IA enzymes: topoisomerase I and III. Topoisomerase III functions as the principal cellular decatenase and participates in efficient chromosome segregation [ 2 , 3 ].

The TOPRIM domain has two conserved motifs, one of which centres at a conserved glutamate and the other one at two conserved aspartates (DxD). For topoisomerases the conserved glutamate is believed to act as a general base in strand joining and, as a general acid in strand cleavage. The DXD motif may co-ordinate Mg2+, a cofactor required for full catalytic function [ 4 ].

1. The mechanism of type IA topoisomerase-mediated DNA topological transformations. Mol. Cell 7, 301-7
2. Topoisomerase III can serve as the cellular decatenase in Escherichia coli. J. Biol. Chem. 278, 8653-60
3. A role for topoisomerase III in Escherichia coli chromosome segregation. Mol. Microbiol. 86, 1007-22
4. Toprim--a conserved catalytic domain in type IA and II topoisomerases, DnaG-type primases, OLD family nucleases and RecR proteins. Nucleic Acids Res. 26, 4205-13