Termination of Translation Chris Avins Elizabeth Durante Christine Noonan

Basic Mechanism 1. Elongation stops when a stop codon reaches A site of ribosome

Basic Mechanism 2. Release factor binds to stop codon

Basic Mechanism 3. Release factor adds H 2 O instead of an amino acid 4. Bond is broken and polypeptide chain is freed

tRNA

Release Factors Basic function: release polypeptide chain from mRNA There are two release factors that work together in order to terminate translation (eRF1 & eRF3 in eukaryotes) (RF1/RF2 & RF3 in prokaryotes)

Eukaryotic Release Factors A stop codon is recognized by the heterodimer complex of eRF1 and eRF3 These release factors mimic tRNA structurally and functionally – eRF3 triggers GTP hydrolysis, enhancing the rate of peptidyl release – It also recycles post-termination ribosomes to 5’ end to begin initiation again

The Termination Signal eRF1 recognizes all three stop codons RF stop codon recognition is up to 60 times slower than sense codon decoding eRF1 accurately discriminates between U-purine- purine codons and other sense codons, interacting with U-purine-purine codons stabilize eRF1 in a conformation to proceed to the next step

The Termination Signal Codons surrounding the stop codons are not random. The tetranucleotide is important in determining the efficiency of termination As many as three succeeding nucleotides may contact the RF and play a role in termination 5’ nucleotide context also influences efficiency

Stop Codon Recognition 8 protein residues found in eRF1 act in the physical interaction of eRF1 and mRNA stop codon that mediate stop codon recognition 5 of the proteins were consistent in all analyzed species 3 of the proteins were only the same in species using the same set of stop codons 2 more proteins need more research Stop codon selection in eukaryotes is not yet understood

Prokaryotic Differences The job done by eRF1 is divided between RF1 and RF2. Both discriminate between A&G at the 2 nd and 3 rd positions of stop codons using the PAT & SPF tripeptides Peptidyl release is independent of RF3 RF3 stimulates the termination rxn. and binds guanine nucleotides but is not codon-specific There is no structural resemblance between RF1/2 and RF3 and eRF1 and eRF3 due to evolutionary origin of translation termination

References C394485/pdf/emboj pdf C394485/pdf/emboj pdf ull/ a.html ull/ a.html 867w3521/fulltext.pdf 867w3521/fulltext.pdf