TERMINATION OF PROTEIN-SYNTHESIS

One of three mRNA codons - UAA, UAG and UGA - is used to signal to the elongating ribosome that translation should be terminated at this poi nt. Upon the arrival of the stop codon at the ribosomal acceptor(A)-si te, a protein release factor (RF) binds to the ribosome resulting in t he peptidyl transferase centre of the ribosome switching to a hydrolyt ic function to remove the completed polypeptide chain from the peptidy l-tRNA bound at the adjacent ribosomal peptidyl(P)-site. In this revie w recent advances in our understanding of the mechanism of termination in the bacterium Escherichia coil will be summarised, paying particul ar attention to the roles of 16S ribosomal RNA and the release factors RF-1, RF-2 and RF-3 in stop codon recognition. Our understanding of t he translation termination process in eukaryotes is much more rudiment ary with the identity of the single eukaryotic release factor (eRF) st ill remaining elusive. Finally, several examples of how the terminatio n mechanism can be subverted either to expand the genetic code (e.g. s elenocysteine insertion at UGA codons) or to regulate the expression o f mammalian retroviral or plant viral genomes will be discussed.