Protein synthesis in E.coli (bacteria) begins by the association of one 30S ribosomal subunit, an mRNA molecule, fMet-tRNA, three proteins known as Initiation Factors (IF) and guanosine 5 triphosphates (GTP). These molecules constitute the 30S pre initiation complex.
Initiation Factors (IF): Proteins that are required for the initiation of a new polypeptide chain.
- Prokaryotic Initiation Factors (PIF): PIF-1 , PIF-2 , PIF-3
Prokaryotic Initiation Factors(PIF)Mass(Dalton)FunctionsPIF-18100Stimulates activity of IF2 and IF3; increases the affinity of the 30 S subunit for other factors.PIF-297300Kinetic effector of 30s initiation complex formation; favours binding of amino acyl tRNAs with blocked αNH2 groups (formylmethionine-tRNA fMet); positions of fMet-tRNA fMet in P site of ribosome.PIF-320700Kinetic effector of 30 S initiation complex formation; shifts equilibrium 70S =30S+50S to the right side, thereby ensuring provision of free 30 S ribosomal subunit for initiation.