Genetic diversity promotes laboratory based evolution and researchers can use mutagenesis and artificial selection to acquire expected phenotypes more frequently. Continuous evolution makes the important steps of laboratory evolution integrated into an uninterrupted cycle, enabling more generations to be evolved and scarcely any human interventions. Phages such as X174, T7 and λ bacteriophages with ideal mutation rates and feasibility to manipulate have been developed as an excellent platform for in vivo continuous evolution. Researchers at Harvard have recently invented an innovative system for the directed evolution of interested biomolecules: phage-assisted continuous evolution (PACE). PACE enables researchers to evolve biomolecules with desired properties within a very short time, which can perform more than 40 rounds of evolution in one day. Up to now, RNAP, protease, gene editing tool, receptor binding protein, aminoacyl-tRNA synthetase and single-chain variable fragments (scFv) have been optimized and evolved with improved activities and specificities by PACE. In addition, two simplified versions of PACE (PRECEL, PANCE) and a novel M13 phagemid-based system have been developed to expand the toolkit of directed evolution. It is promising and exciting that potentially any disease-related molecules which link desired activities with phage propagation can be optimized by above phage-assisted systems, thus leading to more potent biological therapies to be developed and applied into the clinic.
Keywords: PACE; PANCE; continuous evolution; phagemid-based; phages.