Type I topoisomerase

DNA topoisomerase I, N-terminal (non-catalytic), viral
amino terminal 9kda domain of vaccinia virus dna topoisomerase i residues 1-77, experimental electron density for residues 1-77
Identifiers
SymbolVirDNA-topo-I_N
PfamPF09266
InterProIPR015346
SCOP21vcc / SCOPe / SUPFAM
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary

In molecular biology Type I topoisomerases are enzymes that cut one of the two strands of double-stranded DNA, relax the strand, and reanneal the strand. They are further subdivided into two structurally and mechanistically distinct topoisomerases: type IA and type IB.

  • Type IA topoisomerases change the linking number of a circular DNA strand by units of strictly 1.
  • Type IB topoisomerases change the linking number by multiples of 1 (n).

Historically, type IA topoisomerases are referred to as prokaryotic topo I, while type IB topoisomerases are referred to as eukaryotic topoisomerase. This distinction, however, no longer applies as type IA and type IB topoisomerases exist in all domains of life.

Functionally, these subclasses perform very specialized functions. Prokaryotic topoisomerase I (topo IA) can only relax negative supercoiled DNA, whereas eukaryotic topoisomerase I (topo IB) can introduce positive supercoils, separating the DNA of daughter chromosomes after DNA replication, and relax DNA.