ABSTRACT
Eukaryotic ribosomes are larger and more complex than prokaryotic ribosomes. Initiation is basically similar in prokaryotes and eukaryotes except that in eukaryotes at least nine initiation factors are involved, the initiating amino acid is methionine, eukaryotic mRNAs do not contain Shine — Dalgarno sequences, and eukaryotic mRNA is monocistronic. The overall mechanism of protein synthesis in eukaryotes is basically the same as in prokaryotes, with three phases defined as initiation, elongation and termination. Elongation in eukaryotes requires three eukaryotic initiation factors that have similar functions to the corresponding prokaryotic proteins. During elongation in bacteria, the deacylated tRNA in the P site moves to the E site prior to leaving the ribosome. In eukaryotes, eukaryotic release factor eRF-1 recognizes all three termination codons (UAA, UAG and UGA) and, with the help of protein eRF-3, terminates translation.
