Functions of Eukaryotic Factors in Initiation of Translation

Initiation of protein synthesis in both eukaryotes andprokaryotes involves the assembly by initiation factors ofseparated large and small ribosome subunits into a ribosomal initiation complex in which initiator tRNA is positioned in the ribosomal P site so that it is base-paired withthe initiation codon of the mRNA. In prokaryotes, thesmall (30S) ribosomal subunit binds directly to the initiation codon region, and initiation involves only three single-subunit initiation factors termed IF1, IF2, and IF3.The initiation process in eukaryotes is significantly morecomplex than this; it may involve more than ten eukaryotic initiation factors (eIFs), and on most mRNAs, thesmall (40S) ribosomal subunit first binds to the 5′ end ofan mRNA and then scans downstream searching for theinitiation codon...