DNA unknotting activity (DNA topoisomerase II) isolated from a thermophilic archaebacterium Sulfolobus is inhibited by novobiocin. Partial purification, identification of the two subunits and characteristics of the enzyme.
DNA topoisomerases II are enzymes which have been purified from a lot of organisms and have been found to be involved in segregation of chromosomes. The following article reports the analysis of a partially purified DNA topoisomerase II from Sulfolobus (strain B12) a thermophilic archaebacterium which grows at 80 degrees C. The enzyme is composed by two subunits: the A subunit with a molecular mass of 85,000 Da which contains the nicking-closing activity and the B subunit with a molecular mass of 65,000 Da which contains the ATP binding site. The enzyme relaxes negatively as well as positively supercoiled DNA consequently to ATP hydrolysis into ADP (as eukaryotic DNA topoisomerases II and Escherichia coli DNA topoisomerase IV do). DNA relaxation catalyzed by the thermophilic enzyme is inhibited in the presence of both bacterial antibiotics acting at the ATP binding site such as novobiocin and coumermycin A1 at the concentration which was found to inhibit the E. coli type II DNA topoisomerases (DNA gyrase and DNA topoisomerase IV). Based on the relaxation of both negatively and positively supercoiled DNA and the sensitivity to antibiotics such as novobiocin and coumermycin A1, the DNA topoisomerase II isolated from thermophilic archaebacterium shares common characteristics with E. coli DNA topoisomerase II.