An important consideration for the expression of cloned genes in recombinant expression systems is the ability of the foreign host to produce the protein faithfully in a form that is similar or identical to that found in the cell type from which the gene was cloned. For eukaryotic proteins, this frequently involves many posttranslational modifications of the protein, such as glycosylation, phosphorylation, processing, and secretory events. Additionally, very precise interactions are essential for the correct folding of the polypeptide to achieve the final tertiary structure. If the folding is incorrect, then the molecule will often be biologically inactive.
