Functions of Prokaryotic Initiation Factors

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)	Functions
  PIF-1	8100	Stimulates activity of IF2 and IF3; increases the affinity of the 30 S subunit for other factors.
  PIF-2	97300	Kinetic 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-3	20700	Kinetic 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.