title: An evolutionary ratchet leading to loss of elongation factors in eukaryotes.
abstract: BACKGROUND
  The GTPase eEF1A is the eukaryotic factor responsible for the essential, universal function of aminoacyl-tRNA delivery to the ribosome. Surprisingly, eEF1A is not universally present in eukaryotes, being replaced by the paralog EFL independently in multiple lineages. The driving force behind this unusually frequent replacement is poorly understood.
  
  
  RESULTS
  Through sequence searching of genomic and EST databases, we find a striking association of eEF1A replacement by EFL and loss of eEF1A's guanine exchange factor, eEF1Bα, suggesting that EFL is able to spontaneously recharge with GTP. Sequence conservation and homology modeling analyses indicate several sequence regions that may be responsible for EFL's lack of requirement for eEF1Bα.
  
  
  CONCLUSIONS
  We propose that the unusual pattern of eEF1A, eEF1Bα and EFL presence and absence can be explained by a ratchet-like process: if either eEF1A or eEF1Bα diverges beyond functionality in the presence of EFL, the system is unable to return to the ancestral, eEF1A:eEFBα-driven state.
authors.affiliation: University of Tartu, Institute of Technology, Nooruse 1, 50411 Tartu, Estonia. Gemma.atkinson@ut.ee.
authors.forename: Gemma C
authors.initials: GC
authors.lastname: Atkinson
authors.forename: Anton
authors.initials: A
authors.lastname: Kuzmenko
authors.forename: Ivan
authors.initials: I
authors.lastname: Chicherin
authors.forename: Axel
authors.initials: A
authors.lastname: Soosaar
authors.forename: Tanel
authors.initials: T
authors.lastname: Tenson
authors.forename: Martin
authors.initials: M
authors.lastname: Carr
authors.forename: Piotr
authors.initials: P
authors.lastname: Kamenski
authors.forename: Vasili
authors.initials: V
authors.lastname: Hauryliuk
mesh_terms: D000595:Amino Acid Sequence; D001105:Archaea / Q000235:genetics; D001419:Bacteria / Q000235:genetics; D017124:Conserved Sequence; D056890:Eukaryota / Q000235:genetics*; D019143:Evolution, Molecular; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010445:Peptide Elongation Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D010445:Peptide Elongation Factors