TopoIA_RevGyr : The topoisomerase-primase (TORPIM) domain found in members of the type IA family of DNA topoisomerases (Topo IA) similar to the ATP-dependent reverse gyrase found in archaea and thermophilic bacteria. 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. Reverse gyrase is also able to insert positive supercoils in the presence of ATP and negative supercoils in the presence of AMPPNP. The TOPRIM domain has two conserved motifs, one of which centers 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.
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