>TIGR01056 topB DNA topoisomerase III; InterPro: IPR005738 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 , . DNA topoisomerases are divided into two classes: type I enzymes (5.99.1.2 from EC; topoisomerases I, III and V) break single-strand DNA, and type II enzymes (5.99.1.3 from EC; topoisomerases II, IV and VI) break double-strand DNA . 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 describes topoisomerase III from bacteria and its equivalent encoded on plasmids. In Escherichia coli, topoisomerase III functions as the principal cellular decatenase, capable of unlinking replicating daughter chromosomes . Topoisomerase III requires single-stranded DNA for binding, so it is more efficient at decatenating chromosomes if the DNA circles contain a small gap. It appears that Topoisomerase III works by removing precatenanes, an alternative form that can be taken by the positive linkages that arise between the daughter chromosomes during replication. Topoisomerase III shows considerable identity to bacterial topoisomerase I, except that it lacks the zinc finger region found in the latter. More information about this protein can be found at Protein of the Month: DNA Topoisomerase .; GO: 0003677 DNA binding, 0003916 DNA topoisomerase activity, 0006265 DNA topological change, 0006268 DNA unwinding during replication, 0005694 chromosome.

Probab=94.24  E-value=0.12  Score=32.51  Aligned_cols=62  Identities=32%  Similarity=0.445  Sum_probs=47.7

Q ss_pred             HHHHHHHCCCCCCEEEEEECCCCCHHHHHHHHHHHHCCCC---CEEEEEECCCCCCCCHHHHHHHHHHHHHHC
Q ss_conf             9999985157855499994699786899999999820179---808874146748820666347999999830
Q gi|254780762|r  128 QSLIERIEVKKIRELIFAISATIEGQTTAHYIMDKLKGID---VKITRLAYGIPMGSELDYLDDGTIFEAIRS  197 (201)
Q Consensus       128 ~~L~~ri~~~~i~EVIlA~~~t~EGe~Ta~yi~~~lk~~~---ikitrla~GiP~G~~ley~D~~TL~~Al~~  197 (201)
T Consensus        94 n~ik~~L~~~~v~evviATDa~REGe~ia~~iL~~~~~~~ek~~~v~RLw--------~~~~~~~ai~~A~~~  158 (755)
T TIGR01056        94 NVIKRLLKEKEVDEVVIATDADREGELIAREILDYLKVRDEKKVRVKRLW--------ISSLDDKAIRKAFKK  158 (755)
T ss_pred             HHHHHHHHHCCCCEEEECCCCCCHHHHHHHHHHHHHCCCCCCCEEEEEEE--------ECCCCHHHHHHHHHH
T ss_conf             99997631137572787268863257999999987516856530578873--------013787899999985