page_title: Directed evolution
section_title: Ensuring heredity
hierarchical_section_title: Directed evolution / Principles / Ensuring heredity
caption_attribution_description: English: An expressed protein can either be covalently linked to its gene (as in mRNA, left) or compartmentalized with it (cells or artificial compartments, right). Either way ensures that the gene can be isolated based on the activity of the encoded protein.
context_page_description: Directed evolution is a method used in protein engineering that mimics the process of natural selection to steer proteins or nucleic acids toward a user-defined goal. It consists of subjecting a gene to iterative rounds of mutagenesis, selection and amplification. It can be performed in vivo, or in vitro. Directed evolution is used both for protein engineering as an alternative to rationally designing modified proteins, as well as studies of fundamental evolutionary principles in a controlled, laboratory environment.
context_section_description: When functional proteins have been isolated, it is necessary that their genes are too, therefore a genotype-phenotype link is required. This can be covalent, such as mRNA display where the mRNA gene is linked to the protein at the end of translation by puromycin. Alternatively the protein and its gene can be co-localised by compartmentalisation in living cells or emulsion droplets. The gene sequences isolated are then amplified by PCR or by transformed host bacteria. Either the single best sequence, or a pool of sequences can be used as the template for the next round of mutagenesis. The repeated cycles of Diversification-Selection-Amplification generate protein variants adapted to the applied selection pressures.
caption: An expressed protein can either be covalently linked to its gene (as in mRNA, left) or compartmentalized with it (cells or artificial compartments, right). Either way ensures that the gene can be isolated based on the activity of the encoded protein.
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