ABSTRACT
During translation the mRNA is read in a 5' to 3' direction and protein is made in an N-terminal to C-terminal direction. Translation relies upon aminoacyl-tRNAs that carry specific amino acids and recognize the corresponding codons in mRNA by anticodon–codon base pairing. Translation takes place in three phases; initiation, elongation and termination. Initiation of protein synthesis requires proteins called initiation factors (IFs). In prokaryotes, three initiation factors (IF-1, IF-2 and IF-3) are essential. At the start of the first round of elongation the initiation codon (AUG) is positioned in the P site with fMet-tRNAfMet bound to it via codon–anticodon base pairing. Eventually, one of three termination codons becomes positioned in the A site. These are UAG, UAA and UGA. Each prokaryotic ribosome, shown schematically has several binding sites for tRNAs. The aminoacyl-tRNA binding siten is where, during elongation, the incoming aminoacyl-tRNA binds.
