This model describes reverse gyrase, found in both archaeal and bacterial thermophiles. This enzyme, a fusion of a type I topoisomerase domain and a helicase domain, introduces positive supercoiling to increase the melting temperature of DNA double strands. Generally, these gyrases are encoded as a single polypeptide. An exception was found in Methanopyrus kandleri, where enzyme is split within the topoisomerase domain, yielding a heterodimer of gene products designated RgyB and RgyA. [DNA metabolism, DNA replication, recombination, and repair]
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