ATP-independent DNA topoisomerase from Fervidobacterium islandicum

Abstract Thermotogales are thermophilic eubacteria belonging to a very slowly evolving branch in the eubacterial tree. In this report, we describe the purification and characterization of an ATP-independent DNA topoisomerase from the Thermotogale, Fervidobacterium islandicum . The enzyme, a monomer of about 75 kDa, is a type I DNA topoisomerase sharing many properties with the other bacterial topoisomerases I: it absolutely requires Mg 2+ for activity, relaxes negatively but not positively supercoiled DNA and is inhibited by single-stranded M13 DNA and spermidine. A feature of the F. islandicum ATP-independent DNA topoisomerase I is its thermophily. The optimal temperature for the enzymatic activity is 75°C. Studies about thermostability show that the enzyme is more stable when incubated undiluted in the storage buffer. In these conditions, 60% activity was retained after a 30 min preincubation at 75°C.