Crystal structure of the eukaryotic 40S ribosomal subunit in complex with eIF1

Ribosomes are large cellular ribonucleoprotein assemblies, which are responsible for protein synthesis. The eukaryotic ribosome is composed of two unequal subunits, the small 40S subunit, which is involved with the early steps of translation initiation and the large 60S subunit. We determined the crystal structure of the Tetrahymena thermophila 40S subunit in complex with translation initiation factor eIF1 to a resolution of 3.9Å (1). The resulting model contains the ribosomal RNA as well as all ribosomal proteins of the small subunit and the initiation factor. In general, proteins are more prominent in the eukaryotic ribosome when compared to the bacterial ribosome. This is especially marked at the beak structure, which has transformed from an all-RNA structure in the bacterial ribosome to a protein feature in eukaryotic 40S. Since the structure and postion of ribosomal proteins rpS6e and RACK1 are resolved, insights into eukaryote specific regulation and signaling at the ribosome are gained. In addition, the position of eIF1 at the ribosome suggests a mechanism for eIF1 involvement into the early steps of initiation, especially start codon recognition.

Crystal structure of 40S:eIF1 complex