Domain IV of prokaryotic Initiation Factor 2 and archaeal and eukaryotic Initiation Factor 5
This family represents the domain IV of prokaryotic Initiation Factor 2 (IF2) and its archaeal and eukaryotic homologs IF5B. IF2, the largest initiation factor is an essential GTP binding protein. In E. coli three natural forms of IF2 exist in the cell, IF2alpha, IF2beta1, and IF2beta2. Disruption of the eIF5B gene (FUN12) in yeast causes a severe slow-growth phenotype, associated with a defect in translation. eIF5B has a function analogous to prokaryotic IF2 in mediating the joining of the 60S ribosomal subunit. The eIF5B consists of three N-terminal domains (I, II, II) connected by a long helix to domain IV. Domain I is a G domain, domain II and IV are beta-barrels and domain III has a novel alpha-beta-alpha sandwich fold. The G domain and the beta-barrel domain II display a similar structure and arrangement to the homologous domains in EF1A, eEF1A and aeIF2gamma.