Topoisomerase-primase domain. This is a nucleotidyl transferase/hydrolase domain found in type IA, type IIA and type IIB topoisomerases, bacterial DnaG-type primases, small primase-like proteins from bacteria and archaea, OLD family nucleases from bacterial and archaea, and bacterial DNA repair proteins of the RecR/M family. This domain has two conserved motifs, one of which centers at a conserved glutamate and the other one at two conserved aspartates (DxD). This glutamate and two aspartates, cluster together to form a highly acid surface patch. The conserved glutamate may act as a general base in nucleotide polymerization by primases and in strand joining in topoisomerases and, as a general acid in strand cleavage by topisomerases and nucleases. The DXD motif may co-ordinate Mg2+, a cofactor required for full catalytic function.
Comment:involved in both strand cleavage and rejoining
Comment:reaction is Mg2+ dependent
Comment:catalytic mechanism of ssDNA cleavage in 1I7D_A: active site tyrosine forms a covalent linkage with the 5' phosphate of the scissile bond and conserved glutamate of TOPRIM domain donates a proton to the leaving 3' oxygen of the scissile bond
Structure:1I7D_A; Escherichia coli topoisomerase III with bound ssDNA, contacts at 3.5A - View structure with Cn3D