<p>This domain is found in several ATP-binding proteins for example: histidine kinase, DNA gyrase B, topoisomerases [<cite idref="PUB00022659"/>], heat shock protein HSP90 [<cite idref="PUB00031400"/>, <cite idref="PUB00031884"/>, <cite idref="PUB00031942"/>], phytochrome-like ATPases and DNA mismatch repair proteins. The fold of this domain consists of two layers, alpha/beta, which contains an 8-stranded mixed beta-sheet.</p><p>More information about this protein can be found at Protein of the Month: DNA Topoisomerase [<cite idref="PUB00035961"/>].</p>