Filogenômica das topoisomerases do DNA: suas origens e papeis putativos na emergência dos organismos modernos

• Phylogenomics of DNA topoisomerases: their origin and putative roles in the emergence of modern organisms
  
  
  Patrick Forterre and Danièle Gadelle*
  
  
  -Author Affiliations
  
  
  Institut de Génétique et Microbiologie, Univ Paris-Sud, 91405 Orsay Cedex, France CNRS UMR 8621 and Institut Pasteur, 75015 Paris, France
  
  
  *To whom correspondence should be addressed. Tel: +0033169156445; Fax:+0033169157808; Email: daniele.gadelle@igmors.u-psud.fr
  
  
  Received October 31, 2008.
  Revision received January 12, 2009.
  Accepted January 12, 2009.
  
  
  Abstract
  
  
  Topoisomerases are essential enzymes that solve topological problems arising from the double-helical structure of DNA. As a consequence, one should have naively expected to find homologous topoisomerases in all cellular organisms, dating back to their last common ancestor. However, as observed for other enzymes working with DNA, this is not the case. Phylogenomics analyses indicate that different sets of topoisomerases were present in the most recent common ancestors of each of the three cellular domains of life (some of them being common to two or three domains), whereas other topoisomerases families or subfamilies were acquired in a particular domain, or even a particular lineage, by horizontal gene transfers. Interestingly, two groups of viruses encode topoisomerases that are only distantly related to their cellular counterparts. To explain these observations, we suggest that topoisomerases originated in an ancestral virosphere, and that various subfamilies were later on transferred independently to different ancient cellular lineages. We also proposed that topoisomerases have played a critical role in the origin of modern genomes and in the emergence of the three cellular domains.
  
  
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