Eukaryotic Translation-Elongation & Termination

Main Body

Dr.V.Malathi

The sequence of steps in the process of elongation are :

•Movement of ribosome to next codon

•Incoming aminoacyl tRNA brought to the ribosome by eEF-1α- GTP.

•GTP hydrolysed

•eEF-1α- GDP- complex dissociates

•GDP/ GTP exchange for additional translocations.( carried out by eEF-1 βγ).

•Peptide in ribosome P-site transferred to aminoacyl-tRNA in A site.

•Reaction called Transpeptidation ; catalysed by peptidyl transferase.

•Peptidyl tRNA movement from A site to P site called –Translocation. Catalyzed by eEF-2: coupled to GTP hydrolysis

•In the process of translocation- Ribosome moved to next codon of mRNA resides in the A site.

•eEF-2 released. Cycle begins again.

Regulation

•Ability of eEF-2 to carry out translocation is regulated by state of Phosphorylation

•When phosphorylated enzyme is inhibited

•Phosphorylation catalyzed by eEF2Kinase (eEF2K).

•eEF2K activated by calcium.

•Phosphorylation of eEF2K by mTOR- master metabolic regulatory Kinase – inactivates eEF2K

•Requires releasing factors – eRFs

•Termination signal – UAG, UAA and UGA

•eRF binds to A site along with GTP

•This binding stimulates peptidyl transferase activity to transfer the peptidyl group to water

•Uncharged t RNA left in p site expelled with GTP hydolysis

•80S complex dissociates

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