UNIVERSALLY CONSERVED TRANSLATION INITIATION-FACTORS

The process by which translation is initiated has long been considered similar in Bacteria and Eukarya but accomplished by a different unrel ated set of factors in the two cases. This not only implies separate e volutionary histories for the two but also implies that at the univers al ancestor stage, a translation initiation mechanism either did not e xist or was of a different nature than the extant processes, We demons trate herein that (i) the ''analogous'' translation initiation factors IF-1 and eIF-1A are actually related in sequence, (ii) the ''eukaryot ic'' translation factor SUI1 is universal in distribution, and (iii) t he eukaryotic/archaeal translation factor eIF-5A is homologous to the bacterial translation factor EF-P. Thus, the rudiments of translation initiation would seem to have been present in the universal ancestor s tage. However, significant development and refinement subsequently occ urred independently on both the bacterial lineage and on the archaeal/ eukaryotic line.