Mechanisms of DNA synthesis and topoisomerisation in archaebacteria — Reverse gyration in vitro and in vivo

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Summary DNA replication in halophilic archaebacteria is inhibited in vivo by aphidicolin and etoposide, which are specific inhibitors of eukaryotic DNA polymerase a and DNA topoisomerase II respectively. This suggests that the replication machinery of archaebacteria shares features with that of eukaryotes. DNA replication in halobacteria is inhibited by coumarins at doses which specifically inhibit eubacterial DNA gyrase. The archaebacterial type II DNA topoisomerase therefore also displays eubacterial feature. We have isolated a DNA polymerase and a DNA topoisomerase in Sulfolobus acidocaldarius . The topoisomerase introduces positive supertwists in a relaxed DNA at the expense of ATP. This new enzyme, called reverse gyrase, has never been found in eukaryotes and eubacteria. Reverse gyrase is a type I DNA topoisomerase; this is the first enzyme of this class which exhibits ATP-dependence and gyrase activity. The DNA of the SSV1 virus is positively supercoiled; this finding suggests that reverse gyrase is not only active in vitro but also in vivo in Sulfolobales.