elF3

New Insights Into Protein Synthesis And Hepatitis C Infections: "Protein synthesis in mammalian cells begins with the loading of mRNA onto the small ribosome subunit, 40S, which is, in part, one of the responsibilities of the eIF3 complex. The eIF3 complex also interacts with other translation elements that bind at the start of the mRNA, prevents premature joining of the 40S and 60S ribosomal subunits, and helps assemble active ribosomes. Until now, the structural basis for eIF3's multiple activities has been unknown.

At a resolution of 30 angstroms, the cryo-EM reconstructions of Doudna and Nogales and their collaborators show eIF3 to be a particle consisting of five lobes - analogous to a head, and a pair of arms and legs. The study shows that the left arm of the eIF3 complex binds to the eukaryotic protein complex that recognizes the methylated guanosine cap at the 5’-end of the eukaryotic mRNAs (mRNA consists of a coding region sandwiched between a 5’-end and a 3’-end). By drawing the mRNA’s 5’-end cap through the ribosome entry site and towards the exit, eIF3 ensures the mRNA is properly positioned for its genetic code to be translated.

Acting like a molecular wrestler, eIF3 will also wrap its arms and legs around a structural element of RNA for the hepatitis C virus (HVC), known as the internal ribosome entry site (IRES), and pin it to the exit site of the 40S ribosome subunit. The IRES leaves through the left arm of the eIF3 complex at the same location where interaction with the human mRNA cap-binding complex takes place."