Nc. Kyrpides et Cr. Woese, ARCHAEAL TRANSLATION INITIATION REVISITED - THE INITIATION-FACTOR-2 AND EUKARYOTIC INITIATION-FACTOR 2B ALPHA-BETA-DELTA SUBUNIT FAMILIES, Proceedings of the National Academy of Sciences of the United Statesof America, 95(7), 1998, pp. 3726-3730
As the amount of available sequence data increases, it becomes apparen
t that our understanding of translation initiation is far from compreh
ensive and that prior conclusions concerning the origin of the process
are wrong. Contrary to earlier conclusions, key elements of translati
on initiation originated at the Universal Ancestor stage, for homologo
us counterparts exist in all three primary taxa. Herein, me explore th
e evolutionary relationships among the components of bacterial initiat
ion factor 2 (IF-2) and eukaryotic IF-2 (eIF-2)/eIF-2B, i.e., the init
iation factors involved in introducing the initiator tRNA into the tra
nslation mechanism and performing the first step in the peptide chain
elongation cycle, All Archaea appear to posses a fully functional eIF-
2 molecule, hut they lack the associated GTP recycling function, eIF-2
B (a five-subunit molecule), Yet, the Archaea do posses members of the
gene family defined by the (related) eIF-2B subunits alpha, beta, and
delta, although these are not specifically related to any of the thre
e eukaryotic subunits, Additional members of this family also occur in
some (but by no means all) Bacteria and even in sonic eukaryotes. The
functional significance of the other members of this family is unclea
r and requires experimental resolution, Similarly, tile occurrence of
bacterial IF-2-like molecules in all Archaea and in some eukaryotes fu
rther complicates the picture of translation initiation, Overall, thes
e data lend further support to the suggestion that the rudiments of tr
anslation initiation were present at the Universal Ancestor stage.