DNA TOPOISOMERASE-V IS A RELATIVE OF EUKARYOTIC TOPOISOMERASE-I FROM A HYPERTHERMOPHILIC PROKARYOTE

THE DNA topoisomerases are ubiquitous enzymes that fulfil vital roles in the replication, transcription and recombination of DNA by carrying out DNA-strand passage reactions1-7. Here we characterize a prokaryotic counterpart to the eukaryotic topoisomerase I in the hyperthermophilic methanogen Methanopyrus kandleri8-10. The new enzyme, called topoisomerase V, has the following properties in common with eukaryotic topoisomerase I, which distinguish it from all other known prokaryotic topoisomerases: (1) its activity is Mg2+-independent; (2) it relaxes both negatively and positively supercoiled DNA; (3) it makes a covalent complex with the 3' end of the broken DNA strand; and (4) it is recognized by antibody raised against human topoisomerase I. Eukaryotic-like enzymes have been discovered in some hyperthermophilic prokaryotes, namely the eocytes11 and the extremely thermophilic archaebacteria12, and hyperthermophilic homologues of eukaryotic DNA polymerase-a, transcription factor IIB and DNA ligase13-15 have all been reported. Thus our findings support the idea that some essential parts of the eukaryotic transcription-translation and replication machineries were in place before the emergence of eukaryotes, and that the closest living relatives of eukaryotes may be hyperthermophiles.