Peptide Chain Elongation

Results of studies on protein synthesis in extracts of microbial cells indicate that this process can be divided into three major phases: the initiation, elongation, and termination of the peptide chain (for a review, see Lengyel and Söll, 1969). In the initiation phase, an initiation signal in the messenger RNA (mRNA) specifies the assembly of the components of the translating machinery: attachment to the mRNA of a 30 S ribosomal subunit, of the chain initiator N-formyl-methionyl-tRNAF (F-met-tRNAF), and subsequently, of a 50 S ribosomal subunit. At least three initiation factors and GTP are involved in this phase. During the elongation phase, the ribosome moves along the mRNA (from the 5′ towards the 3′ terminal nucleotide) in steps of 3 nucleotides and attaches one aminoacyl residue to the peptide chain at each step. The peptide chain is linked to tRNA and through this to the ribosome. It is growing from the...