Continuous Evolution of ProteinsIn Vivo

Directed evolution is a vital approach in generating novel therapeutics and biotechnological tools. The three key steps in any directed evolution campaign are diversification of genetic material, translation into functional biomolecules, and selection of fitter variants. The emerging field of continuous directed evolution aims to streamline these steps with engineered systems that require little or no manual staging of the evolutionary process. A shared principle behind these designs is the achievement of genetic systems with exceptionally high mutation rates targeted only to the DNA that encodes the evolving biomolecule of interest while maintaining a normal mutation rate in other DNA. Such targeted rapid mutagenesis technologies support continuous evolution of biomolecules. The systems that we review in this chapter are highly useful in reducing the time and effort required for evolving a wide range of biomolecules. In addition, the evolution systems considered facilitate deeper explorations of sequence space at extensive scale, a consequence of the speed and parallelization of directed evolution enabled by continuous evolution. Continuous evolution therefore increases the likelihood of success in directed evolution campaigns and opens up new areas of investigation, including reaching ambitious biomolecular functions that require long mutational pathways and greater understanding of biomolecular sequence–function relationships.