Enhanced single-base mutation diversity by the combination of cytidine deaminase with DNA-repairing enzymes in yeast.

The occurrence of random mutations can increase the diversity of the genome and promote the evolutionary process of organisms. High efficiency mutagenesis techniques significantly accelerate the evolutionary process. In this work, we describe a targeted mutagenesis system named MutaT7 to significantly increase mutation rate and generate mutations across all four nucleotides in yeast. We constructed different DNA-repairing enzyme-PmCDA1-T7 RNA polymerase (T7 RNAP) fusion proteins, achieved targeted mutagenesis by flanking the target gene with T7 promoters, and tuned the mutation spectra by introducing different DNA-repairing enzymes. With this mutagenesis tool, the proportion of non-C → T mutations was 10-11-fold higher than the cytidine deaminase-based evolutionary tools, and the transversion mutation frequency was also elevated. The mutation rate of the target gene was significantly increased to 5.25 × 10 substitutions per base (s. p. b.). We also demonstrated that MutaT7 could be used to evolve the CrtE, CrtI, and CrtYB gene in the β-carotene biosynthesis process and generate different types of mutations.