Copyright © 1991, American Society for Microbiology Reverse Gyrase in Thermophilic Eubacteria

The presence of reverse gyrase, an unusual ATP-dependent type I topoisomerase first isolated from thermophilic archaebacteria, has been detected in four strains of Thermotogaks, an order of extremely thermophilic eubacteria. This result suggests that reverse gyrase plays a key role in high-temperature-living organisms, independently of the evolutionary kingdom to which they belong. Reverse gyrase is a type I topoisomerase first isolated from a thermophilic archaebacterium, Sulfolobus acidocal-darius (7). This enzyme, fully active at 75°C, catalyzes the introduction of positive supercoils into a closed circular DNA, in an ATP-dependent process (3, 9-11). The discovery of such an unusual enzyme raised the question of its function and distribution within archaebacteria. In a previous study, we have shown that reverse gyrase activity was largely distributed among thermophilic archae-bacteria, suggesting that the enzyme is needed for life at high temperature (1). However, the enzyme seemed restricted t