Protein expression is an essential biotechnological process of producing a specific recombinant protein. Here, we present priciples in protein expression manufacturing.

Protein expression principle

Protein expression is the process by which information from target gene is used in the synthesis of a functional protein, including transcription of DNA to mRNA and translation of mRNA to polypeptide chains.

Transcription: DNA to RNA

 Initiation ◦ Form a complex with transcription factors and RNA polymerase

 Elongation ◦ Open DNA double helix ◦ The RNA polymerase reads one strand and assembles ribonucleotides into a strand of RNA ◦ Inserted ribonucleotides into the growing RNA strand following base pairing rules.

 Termination ◦ RNA synthesis complete and transcript release ◦ In eukaryotes, introns are removed while a cap and multiple adenines are added to generate a polyA tail.

Translation: RNA to polypeptide

 Initiation ◦ The small subunit of the ribosome binds to the 5’ end and identifies the initiation codon ◦ The large subunit of the ribosome joins them and forms a complex

 Elongation ◦ An aminoacyl-tRNA base pair with next codon on mRNA arrives at the A site associated with an elongation factor. ◦ The preceding amino acid link to the incoming ones and forms a peptide bond

 Termination ◦ Occur when the ribosome reaches stop codons recognized by release factors ◦ Release the polypeptide from the ribosome