Microbiology Procedure

Index >> Protein Synthesis >> Binding of the fmet tRNA with mRNA 30S Complex

Protein Synthesis
Protein Synthesis Part 1
Nomenclature of Prokaryotic and Eukaryotic Initiation Factors
Formylation of Methionine
Starting Amino Acids, Initiation tRNAs and Amino acid tRNA Complexes of Eukaryotes and Prokaryotes
Formation of the 30S Initiation Complex
Formation of the mRNA-30S Subunit Complex
Binding of fMet-tRNA with mRNA-30S Complex
Elongation Factors
Binding of Aminoacyl tRNA to the A Site
Peptide Bond Formation
Translocation
Role of Ribosomal Proteins
Translocation Reactions
Movement of mRNA

Binding of the fmet tRNA with mRNA 30S Complex

	Binding of the fmet tRNA with mRNA 30S Complex - In prokaryotes the binding of the fMet-tRNA complex with the mRNA-30S subunit comp1ex requires the initiation factors I F-2 and IF-I and GTP. IF-2 is required for recognition and binding of fMet-tRNA. The other initiation factors probably also participate, but IF-2 is the most important. The initiation tRNA with attached N-formylmethionine binds with its UAC anticodon to an AUG codon of mRNA, or rarely, to a GUG or UUG codon. These codons in mRNA are called initiation codons. Some studies, however, suggest that the binding of fMet-1RNA to the 30S subunit normally proceeds that of mRNA (Noll and Noll, 1972; Jay and Kaempfer, 1974).
Although AUG is the initiation codon it is often preceeded by several nucleotides, which probably enable the codon to occupy a specific position for recognition. In eukaryotes the Met-tRNA binds to the 40S ribosomal subunit first and then the mRNA attaches with its AUO initiation codon.
The mRNA strand has many AUG codons. Only one of these, how ever, functions as an initiation codon. What factors determine that, which AUO will function as the initiating codon? One possibility is that the conformation of tRNA is such that most of the AVO triplets are prevented from functioning as initiators. Another possibility is that a specific sequence of nucleotides near AUG is required for it to function as an initiator. The 70S ribosome has two binding sites for tRNA, the amino acyl or acceptor site (A site) and the peptidyl or polymerisation site (P site), also called the donor site. Each ribosome thus functionally accommodates two codons (6 nucleotides ) at a time. The P and the A sites are located in the 50S subunit. fMet-tRNA binds to the P site. All other tRNAs first bind to the A site and then shift to the P site.
Attachment of the large ribosomal subunit to form the complete initiation complex: The next step in prokaryotes is the attachment of the 50S ribosomal subunit to form the complete 70S initiation complex. During this process GTP is converted to GDP + Pi and the initiation factors IF-1 and IF-2 are released for recycling. In eukaryotes attachment of the 60S ribosomal subunit results in the formation of the complete 80S initiation complex.

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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

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