InterPro: IPR015346 DNA topoisomerase I, N-terminal, viral

DNA topoisomerases regulate the number of topological links between two DNA strands (i.e. change the number of superhelical turns) by catalysing transient single- or double-strand breaks, crossing the strands through one another, then resealing the breaks. These enzymes have several functions: to remove DNA supercoils during transcription and DNA replication; for strand breakage during recombination; for chromosome condensation; and to disentangle intertwined DNA during mitosis [1, 2]. DNA topoisomerases are divided into two classes: type I enzymes (EC:5.99.1.2; topoisomerases I, III and V) break single-strand DNA, and type II enzymes (EC:5.99.1.3; topoisomerases II, IV and VI) break double-strand DNA [3].

Type I topoisomerases are ATP-independent enzymes (except for reverse gyrase), and can be subdivided according to their structure and reaction mechanisms: type IA (bacterial and archaeal topoisomerase I, topoisomerase III and reverse gyrase) and type IB (eukaryotic topoisomerase I and topoisomerase V). These enzymes are primarily responsible for relaxing positively and/or negatively supercoiled DNA, except for reverse gyrase, which can introduce positive supercoils into DNA.

This entry represents a domain foundpredominantly found in viral DNA topoisomerase I, a type IB enzyme. This domain assumes a beta(2)-alpha-beta-alpha-beta(2) fold, with a left-handed crossover between strands beta2 and beta3 [4].

More information about this protein can be found at Protein of the Month: DNA Topoisomerase [5].