Microbiology Procedure

Index >> Protein Synthesis >> Formation of the mRNA 30S Subunit 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

Formation of the mRNA 30S Subunit Complex

	Formation of the mRNA 30S Subunit Complex - Messenger RNA (mRNA) becomes attached to the 30S ribosomal subunit to form an mRNA 30S complex. This process requires the initiation factor IF-3.Only one molecule of IF-3 binds to each 30S subunit. It has been suggested that a segment of 16S r RNA in the 30S subunit provides a binding site for IF-3. 16S rRNA is also involved in mRNA binding. Shine and Dalgarno (1974, 1975) have shown that a nucleotide sequence near the 3' end of 16S rRNA base pairs directly with a complementary sequence in mRNA. mRNA molecules contain a sequence of 3-7 purine nucleotides preceeding the initiation codon AUG.
This polypurine sequence on mRNA pairs with a complementary Pol pyrimidine sequence near the 3' end of 16S rRNA. All coliphage RNA ribosome binding sites contain the polypurine sequence 5' AGGAGGU 3' at a similar relative position on the 5' side of the AUG initiation codon. This sequence is complementary to a region near the 3' end of 16S rRNA. It has been suggested that hydrogen bonding between the complementary regions of 16S rRNA and mRNA comprises part of the recognition sequence for chain initiation.IF-3 has several functions
(i) It is essential for binding of mRNA to the 30S subunit. (ii) It affects 30S subunit conformation. (iii) It prevents reassociation of dissociated 30S and 50S subunits.This is important otherwise there would be interference in the formation of the 30S initiation complex. In E. coli, interference factors which bind to IF-3and thus change its specificity, have been isolated.

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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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