<p>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 [<cite idref="PUB00005437"/>]. 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 [<cite idref="PUB00020794"/>, <cite idref="PUB00016842"/>]. DNA topoisomerases are divided into two classes: type I enzymes (<db_xref db="EC" dbkey="5.99.1.2"/>; topoisomerases I, III and V) break single-strand DNA, and type II enzymes (<db_xref db="EC" dbkey="5.99.1.3"/>; topoisomerases II, IV and VI) break double-strand DNA [<cite idref="PUB00020793"/>].</p><p>Type II topoisomerases are ATP-dependent enzymes, and can be subdivided according to their structure and reaction mechanisms: type IIA (topoisomerase II or gyrase, and topoisomerase IV) and type IIB (topoisomerase VI). These enzymes are responsible for relaxing supercoiled DNA as well as for introducing both negative and positive supercoils [<cite idref="PUB00020795"/>].</p><p>This entry represents subunit B of topoisomerase VI, an ATP-dependent type IIB enzyme. Members of this family adopt a structure consisting of a four-stranded beta-sheet backed by three alpha-helices, the last of which is over 50 amino acids long and extends from the body of the protein by several turns. This domain has been proposed to mediate intersubunit communication by structurally transducing signals from the ATP binding and hydrolysis domains to the DNA binding and cleavage domains of the gyrase holoenzyme [<cite idref="PUB00014011"/>]. </p><p>More information about this protein can be found at Protein of the Month: DNA Topoisomerase [<cite idref="PUB00035961"/>].</p> DNA topoisomerase VI, subunit B, transducer