Taxonomic distribution of proteins containing TOPRIM domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing TOPRIM domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Toprim--a conserved catalytic domain in type IA and II topoisomerases, DnaG-type primases, OLD family nucleases and RecR proteins.

Aravind L, Leipe DD, Koonin EV
Nucleic Acids Res. 1998; 26: 4205-13

Iterative profile searches and structural modeling show that bacterial DnaG-type primases, small primase-like proteins from bacteria and archaea, type IA and type II topoisomerases, bacterial and archaeal nucleases of the OLD family and bacterial DNA repair proteins of the RecR/M family contain a common domain, designated Toprim (topoisomerase-primase) domain. The domain consists of approximately 100 amino acids and has two conserved motifs, one of which centers at a conserved glutamate and the other one at two conserved aspartates (DxD). Examination of the structure of Topo IA and Topo II and modeling of the Toprim domains of the primases reveal a compact beta/alpha fold, with the conserved negatively charged residues juxtaposed, and inserts seen in Topo IA and Topo II. The conserved glutamate may act as a general base in nucleotide polymerization by primases and in strand rejoining by topoisomerases and as a general acid in strand cleavage by topoisomerases and nucleases. The role of this glutamate in catalysis is supported by site-directed mutagenesis data on primases and Topo IA. The DxD motif may coordinate Mg2+that is required for the activity of all Toprim-containing enzymes. The common ancestor of all life forms could encode a prototype Toprim enzyme that might have had both nucleotidyl transferase and polynucleotide cleaving activity.

Cloning and analysis of the dnaG gene encoding Pseudomonas putida DNA primase.

Szafranski P, Smith CL, Cantor CR
Biochim Biophys Acta. 1997; 1352: 243-8

The dnaG gene coding for primase, a key enzyme in DNA replication, has been isolated from chromosomal DNA of the soil bacterium Pseudomonas putida. It maps within the putative MMS operon, between the rpsU and rpoD genes. Comparison of the deduced amino acid sequence of P. putida DnaG with sequences of other known bacterial primases reveals the presence of a possible regulatory region which would be unique to pseudomonads. The analysis of nucleotide sequence suggests that stable folding of the dnaG mRNA may significantly contribute to the low level of its expression within a cell.

Three-dimensional structure of the 67K N-terminal fragment of E. coli DNA topoisomerase I.

Lima CD, Wang JC, Mondragon A
Nature. 1994; 367: 138-46

The three-dimensional structure of the 67K amino-terminal fragment of Escherichia coli DNA topoisomerase I has been determined to 2.2 A resolution. The polypeptide folds in an unusual way to give four distinct domains enclosing a hole large enough to accommodate a double-stranded DNA. The active-site tyrosyl residue, which is involved in the transient breakage of a DNA strand and the formation of a covalent enzyme-DNA intermediate, is present at the interface of two domains. The structure suggests a plausible mechanism by which E. coli DNA topoisomerase I and other members of the same DNA topoisomerase subfamily could catalyse the passage of one DNA strand through a transient break in another strand.