Initiation Factors in the Early Events of mRNA Translation in Bacteria

Initiation of mRNA translation in bacteria proceedsthrough several steps. The early events entail the selectionof the mRNA initiation codon by the 30S ribosomal subunit with the help of initiator fMet-tRNA and initiation factors IF1, IF2, and IF3, which all together form a "30S initiation complex." Subsequently, the choice of the start siteis made irreversible by the binding of the 50S ribosomalsubunit to the 30S initiation complex, which expels IF1and IF3 and yields a "70S initiation complex." Among thelate initiation events are the adjustment of fMet-tRNA inthe ribosomal P site, the A-site binding of the EF-Tuternary complex carrying the elongator aminoacyl-tRNAencoded by the second mRNA codon, and the subsequentformation of the first peptide bond yielding the initiationdipeptide. At this stage, with the first translocation, the ribosome enters the elongation phase...