Domain organization of selected eukaryotic translation initiation factors and their homologs. The individual domains are drawn approximately to scale and are labeled by the acronyms that are indicated in the text. Zn in eIF2β and eIF5 indicates a zinc-ribbon. The additional unlabeled regions in CBP80 and YGR278w represent predicted globular domains that are not found in other proteins. The orange bar at the carboxyl terminus of YGR278w shows the RS repeat segment that is also found in several proteins participating in RNA metabolism. I-patch is an isoleucine-rich hexapeptide repeat domain, and NUCT is a nucleotidyl transferase domain of the sugar-nucleotide diphosphate-transferase family (Koonin 1999).