InterPro domain: IPR034149

This topoisomerase-primase (TOPRIM) domain is found in members of the type IA family of DNA topoisomerases (Topo IA) similar to Escherichia coli DNA topoisomerase I. 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 ]. E. coli DNA topoisomerase I is primarily involved in the relaxation of negatively supercoiled DNA by the stand passage mechanism [ 2 ].

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 Mg ²⁺ , a cofactor required for full catalytic function [ 3 ].

1. The mechanism of type IA topoisomerase-mediated DNA topological transformations. Mol. Cell 7, 301-7
2. Type IA DNA topoisomerases: strictly one step at a time. Proc. Natl. Acad. Sci. U.S.A. 99, 11998-2000
3. 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