title: Evolutionary relationship between translation initiation factor eIF-2gamma and selenocysteine-specific elongation factor SELB: change of function in translation factors.
abstract: Eubacterial and eukaryotic translation initiation systems have very little in common, and therefore the evolutionary events that gave rise to these two disparate systems are difficult to ascertain. One common feature is the presence of initiation, elongation, and release factors belonging to a large GTPase superfamily. One of these initiation factors, the gamma subunit of initiation factor 2 (eIF-2gamma), is found only in eukaryotes and archaebacteria. We have sequenced eIF-2gamma gene fragments from representative diplomonads, parabasalia, and microsporidia and used these new sequences together with new archaebacterial homologues to examine the phylogenetic position of eIF-2gamma within the GTPase superfamily. The archaebacterial and eukaryotic eIF-2gamma proteins are found to be very closely related, and are in turn related to SELB, the selenocysteine-specific elongation factor from eubacteria. The overall topology of the GTPase tree further suggests that the eIF-2gamma/SELB group may represent an ancient subfamily of GTPases that diverged prior to the last common ancestor of extant life.
authors.affiliation: Plant Cell Biology Research Centre, Botany School, University of Melbourne, Parkville VIC 3052, Australia. pkeeling@bio.indiana.edu
authors.forename: P J
authors.initials: PJ
authors.lastname: Keeling
authors.forename: N M
authors.initials: NM
authors.lastname: Fast
authors.forename: G I
authors.initials: GI
authors.lastname: McFadden
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001419:Bacteria / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D015852:Eukaryotic Initiation Factor-2 / Q000235:genetics*; D019143:Evolution, Molecular; D020963:GTP Phosphohydrolase-Linked Elongation Factors / Q000235:genetics; D016829:Giardia lamblia / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D016818:Nosema / Q000235:genetics; D010445:Peptide Elongation Factors / Q000235:genetics*; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D016834:Trichomonadida / Q000235:genetics; D014246:Trichomonas vaginalis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D015852:Eukaryotic Initiation Factor-2; D010445:Peptide Elongation Factors; C061878:SelB protein, Bacteria; D020963:GTP Phosphohydrolase-Linked Elongation Factors