The initiator tRNA carries a N-formyl-methionine (fMet) that interacts with the AUG codon of the mRNA. This fMet is the first amino acid in the proteins in *E.coli*.

tRNA with N-formyl-methionine 

The sequence upstream of the first codon in the mRNA is the Shine-Delgarno sequence. It is site that the 30S ribosome interacts with that recruits the binding of the 50S subunit in *E.coli*. This forms an intact ribosome and the initiation complex.

Shine-Delgarno Sequence

The *E. coli* ribosome has been well studied and is the model for prokaryotic transcription. The *E. coli* ribosome has two subunits: the 30S and the 50S. In translation initiation, the 30S recognizes the Shine-Delgarno sequence and then the 50S subunit can interact with the 30S to form the assembled ribosome for translation.

*E. coli* Ribosome

The initiation complex begins translation of proteins. In *E.coli*, the 30S ribosome interacts with the mRNA template, along with initiation factors. 
Guanosine triphosphate is needed as energy for this process. Initiation of translation requires formylated methionines to begin.  

Key terms for translation initiation in prokaryotes: 
1. tRNA N-formyl-methionine (fMet-tRNA^fMet)
2. Shine-Delgarno sequence

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Translation is very similar for prokaryotes and eukaryotes with a few differences. Importantly, translation can occur simultaneously with transcription in prokaryotes, but this does not happen in eukaryotes because of the nucleus.

Translation in Prokaryotes

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Initiation of Translation in Prokaryotes

After the fMet-tRNA^fMet in initiation is in the P site of the ribosome, the A site is free to begin transcription elongation. Elongation progresses with ribosomal translation events that read one codon at a time. 
tRNAs enter the A site and shift to the P site, and exit through the E site for elongation.

Elongation of Translation in Prokaryotes

Translation ends when the ribosome interacts with a nonsense codon which has no associated tRNA. After aligning with the A-site of the ribosome, nonsense codons are recognized by release factors and cause the P-site amino acid to be removed from the P-site to release the newly synthesized protein. The ribosomal subunits dissociate from the mRNA as well. 

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