Microbiology Procedure

Index >> Protein Synthesis >>Release of Polypeptide Chain

Release of Polypeptide Chain

	Release of Polypeptide Chain - Even after termination the polypeptide chain remains bound to the tRNA molecule. The termination codon provides signals to the ribosomes for attachment of release factors In prokaryotes there are three release factors, RF-I, RF-2 and RF-3. (i) RF-l is a single polypeptide chain with a molecular weight of 44,000. It recognizes the termination codons UAA and UAG. About 500 molecules of EF-I are present in one E.coli cell (ii) RF-2 (MW 47,000) recognizes the termination codons UAA and UGA. About 700 molecules of RF-2 are present in one E.coli cell.
(iii) RF-3 (MW 46,000) has no release activity. It stimulates the binding and release of RF-I and RF-2 from the ribosome. Because of this activity it has also been called the stimulatory factor or S factor. The release factors interact with peptidyl transferase causing hydrolysis of the Polypeptide chain at the P site. This results in cleavage and release of the chain from the tRNA molecule at the P site. The residual tRNA is now discharged from the P site. If no further cistrons are to be translated, the ribosome dissociates into its 305 and 50S subunits. In prokaryotes there is no absolute requirement of GTP for release of the polypeptide chain.
In eukaryotes a single release factor (RF) recognizes all the termination codons (UAA, UAG and UGA). In rabbit reticulocytes molecular weights of 56,500 and 115,000 have been ascribed to RF by employing different techniques. This suggests that the RF exists as a dimer of two units. It is not clear whether the monomer or the dimer interacts with the ribosome. The first step in chain termination is the binding of the RF to the A site containing a termination codon. This step requires GTP and activates the peptidyl transferase system. Hydrolysis of peptidyl-tRNA at the P site results in the release of the polypeptide chain from the ribosome. GTP hydrolysis results in the dissociation of the RF from the ribosome. The released RF is recycled.

	Back to Home
Protein Synthesis Part 1 Release of Deacylated tRNA Hydrolysis of GTP Locking and Unlocking Ribosome Model inchworn Theory Conformational Changes Recognition of the Termination Signal Release of the Polypeptide Chain Prokaryote and Eukaryote Release Factors Processing Polypeptide Chain Rate of Protein Synthesis Signal Hypothesis Prokaryote and Eukaryote Protein Synthesis Teminism

Home | Site map | Submit Article | Resources | Search

Language >> English | Français | Español | Deutsch | Italiano | Portugues | Japanese | Korean | Sim-Chinese