As recently reported in Nature, investigators Matthias Fischer and Curtis Suttle from the University of British Columbia have discovered and characterized a new virophage named Mavirus (Maverick virus) and go on to propose an evolutionary link between these virophages and the origins of DNA transposons . Mavirus parasitizes the giant Cafeteria roenbergensis virus (CroV) which has the largest genome of any virus currently known at ~730kb. CroV in turn replicates within its host Cafeteria roenbergensis, a marine zooplankton.
They observe that gene expression in this much smaller virus, at 19kb,is determined by kinetics of CroV transcription machinery. They also find a number of sequence similarities to Mimivirus's own virophage, Sputnik, including several homologous genes including capsid proteins, an ATP-ase, a cysteine protease, and endonuclease/zinc-ribbon protein. Upon further investigation, they determined that a closer genetic and evolutionary relationship exists between Mavirus's predicted protein-coding sequences and Maverick or Polinton (MP) transposable elements (TE). These MPTEs are a class of large transposable elements that are 9-22kb long, encode up to 20 genes, and are found in a wide range of eukaryotes.The authors provide evidence that Mavirus and MPTEs have fairly high homology between their genome structures, lengths and content, suggesting evolution from a common ancestor.
Fischer M., Suttle C. 2011. A Virophage at the Origin of Large DNA Transposons. Science. DOI: 10.1126/science.1199412. Published Online 3 March 2011