Archaeal and eukaryal translation initiation factor 1 differ in their RNA interacting loops

The archaeal translation initiation factor 1 ( aIF 1) is reported to be functionally homologous to the eukaryotic translation initiation factor 1 ( eIF 1). However, lack of a structural comparison between aIF 1 and eIF 1 has limited our understanding of the structural (dis)similarities. Herein, we have determined the three‐dimensional crystal structure of an open reading frame PH 1771.1 encoding aIF 1 in Pyrococcus horikoshii OT 3. Results reveal that although aIF 1 has low sequence similarity with eIF 1, high structural homology exists between the two proteins. Nonetheless, notable critical differences between aIF 1 and eIF 1 could still be perceived at the β 1 –β 2 basic loop, the acidic loop and the solvent‐exposed surface. These differences might lead to a slightly divergent mode of action of aIF 1 during archaeal translation initiation.