Prokaryotic Translation Factors and Mechanisms

Study Notes

Initiation Factors

Prokaryotic initiation factors:
- IF1 (initiation factor 1): helps in the assembly of the initiation complex
- IF2 (initiation factor 2): binds to the 30S subunit and facilitates binding of fMet-tRNA
- IF3 (initiation factor 3): prevents the binding of the 50S subunit to the 30S subunit before initiation is complete
Roles of initiation factors:
- Recognition of the Shine-Dalgarno sequence
- Binding of fMet-tRNA to the start codon
- Formation of the initiation complex

MRNA Stability

MRNA stability affects translation:
- MRNA degradation rates influence the amount of protein synthesized
- MRNA stability is regulated by:
  - RNA-binding proteins
  - 5' and 3' untranslated regions (UTRs)
  - Secondary structure of MRNA
Mechanisms of MRNA degradation:
- Exoribonucleases (e.g., RNase II)
- Endoribonucleases (e.g., RNase E)

Protein Synthesis Inhibitors

Antibiotics that inhibit prokaryotic translation:
- Aminoglycosides (e.g., streptomycin): interfere with initiation and misread MRNA
- Tetracyclines: bind to the 30S subunit and prevent aminoacyl-tRNA binding
- Macrolides (e.g., erythromycin): inhibit translocation of the ribosome
Other inhibitors:
- Chloramphenicol: inhibits peptidyl transferase activity
- Puromycin: mimics aminoacyl-tRNA and prematurely terminates protein synthesis

Translational Coupling

Definition: the process by which the translation of one gene is dependent on the translation of another gene
Mechanisms:
- Overlapping genes: genes that share the same MRNA sequence
- Polycistronic MRNAs: single MRNA encoding multiple genes
- Regulatory elements: sequences that regulate translation initiation

Ribosome Binding

Ribosome binding sites (RBS):
- Shine-Dalgarno sequence: a conserved sequence upstream of the start codon
- SD-augmented RBS: additional sequences that enhance ribosome binding
Mechanism of ribosome binding:
- The 30S subunit binds to the RBS
- The 50S subunit binds to the 30S subunit, forming the 70S initiation complex

Description

Learn about the initiation factors, mRNA stability, protein synthesis inhibitors, translational coupling, and ribosome binding in prokaryotic translation. Understand the mechanisms and processes involved in this complex process.