EVOLUTION OF DNA TOPOISOMERASES AND DNA-POLYMERASES - A PERSPECTIVE FROM ARCHAEA

We review our present knowledge on DNA topoisomerase and DNA polymeras e evolution, with emphasis on information obtained by studying these e nzymes in Archaea. Two archaeal DNA topoisomerase genes have been sequ enced: the reverse gyrase from Sulfolobus acidocaldarius turns out to be a completely novel type of enzyme, likely originating from the fusi on of a helicase and a type I DNA topoisomerase, whereas a novobiocin sensitive type II DNA topoisomerase from Haloferax is closely related to bacterial DNA gyrases. Beside reverse gyrase, we recently isolated from Sulfolobus shibatae a type II DNA topoisomerase which has no gyra se activity and exhibits the pattern of drug sensitivity specific for its eukaryotic counterpart. Several archaeal DNA polymerase genes have now been sequenced: they all belong to the DNA polymerase B family, t ogether with the three eucaryal DNA replicases and Escherichia coli DN A pol II, a repair enzyme. All DNA polymerases from family B described so far are sensitive to aphidicolin. We present recent data suggestin g that archaeal DNA polymerases resistant to aphidicolin also belong t o family B. Phylogenetic trees of DNA topoisomerases and DNA polymeras es turn out to be all noncongruent with the rRNA tree and exhibit diff erent and unusual topologies. We discuss several hypotheses which can explain this observation and their implications concerning the nature of the last common ancestor to the three domains. We conclude that thi s universal ancestor was probably an advanced member of the DNA world that already contained several DNA polymerases and DNA topoisomerases.